Eh, really? Maybe blues flavored rock. I can’t think of them as straight up blues, but I’m not a fan so I only know the hits. Van Halen is rock, then.
I’m not saying they were Blues, but that’s what they were shooting for. One definition I have seen of Rock is “English boys doing a bad job of replicating American Blues and accidently creating a new genre.”
To me the terms are interchangeable. As Lester Bangs said, the defining characteristic of the genre is attitude.
You’ve got my vote. It’s a distinction without a difference. When Kiss sang “Rock and Roll all night”, they didn’t mean like Chubby Checker.
Blues music was an enormous influence on young English musicians in the 60s. The Rolling Stones, Fleetwood Mac, Cream, Free, and a million others emerged out of John Mayall’s Bluesbreakers or Alexis Korner’s Blues Incorporated. The Moody Blues, for Pete’s sake, started as a blues group.
But by 1970 the blues bands were consigned to a niche of purists. To be successful you had to rock. Take Zeppelin’s history. The Yardbirds were a blues band that discovered that their guitarists could have as much fun playing psychedelic radio-friendly rock as being blues purists, at least after Eric Clapton left to join Mayall, where he met Jack Bruce and they quickly left to form Cream with Ginger Baker who had been in the blues-oriented Graham Bond Organization with Bruce. Cream played the blues in concerts and then began writing their own songs. Once that happened rock took over. (And pop. “Anyone for Tennis”?)
Jeff Beck and Jimmy Page took over for the Yardbirds, who imploded leaving Page to reform them into The New Yardbirds, a name which lasted a second-and-a-half and then became Led Zeppelin (something that they would go over like in Keith Moon’s immortal phrase). I bought their first album. It was like an explosion. Blues songs didn’t explode that way even though half the album was stolen uncredited blues. They had been transformed into something different.
Almost all notable bands to this day start by playing music they grew up with and loved, but then alter with own sensibilities. That white English boys wanted to be black American blues artists is true, but only in the way kids in the 50s wanted to be cowboys. They played the blues and played at the blues, and then grew out of it, just as the rock 'n roll artists of the 50s started with R&B or country or folk or big band or hillbilly music and then rejiggered it into rockabilly and rock ‘n’ roll. Anything else is just glib envy.
They clearly were influenced blues, but, save for a few songs, weren’t really trying to play the blues. I mean, blues has a fairly defined structure to it: 12 bars, I-IV-V chords, songs are usually in the form of a line of the verse, a repeated line of the verse maybe with a minor variation, a conclusion to this line. “You Shook Me” and “I Can’t Quit You Baby” on their first album are straight-up blues. “How Many More Times” can definitely fit into blues, but strays from the standard blues formula. I’d count it.
The guys knew what blues was – they played a few blues songs. But I can’t imagine they were shooting to be a blues band since they played mostly songs that were very clearly not blues. I mean, their opening statement to the world was “Good Times, Bad Times.” It’s got blues-types riffs in it, but the structure, chords, rhythm, everything about the song says blues rock, not blues. If the boys wanted to play blues, they could play blues.
No they meant SEX!
That’s not music they’re talking about. 
Hmm…that puts Sammy Hagar’s “Rock And Roll Weekend” into an entirely different light!
But did they? The Beatles weren’t comparing “rock and roll” to “rock”. They were comparing it to modern jazz, tango, mambo, and conga.
Of course, the Beatles didn’t write this song. Chuck Berry did, back in 1957. So if you accept that rock and roll is different from rock, then rock didn’t exist back when Berry wrote this song.
I can accept the people who prefer a distinction because “rock and roll” has a more vintage sound to it, though “rock” is closely approaching that feeling as well. If someone released a song in a different genre, say country or R&B, one might think a bit differently in the way it’s described. If someone said it had a “rock and roll” sound, I might think it had a bit of a rock-a-billy tempo. But if they said it had a “rock” sound, I might expect guitars with distortion and lots of crashes. .
What do people think about later changes?
Do you feel that stuff like Punk in the seventies, House in the eighties, Grunge in the nineties, or Dubstep in the 2000’s are subgenres of Rock? Or do you feel that some or all of these are separate genres distinct from Rock?
Punk and grunge, certainly; they are often referred to as “punk rock” and “grunge rock,” after all.
I don’t know enough about House or Dubstep to answer for those genres.
There are some popular music styles of the last 40-50 years which are arguably not “rock,” nor do they fit into other “meta-genres” like country, R&B, etc. – rap and hip-hop come to mind, among many others.
Is Britney Spears “rock?” She’s “pop,” for certain, but there are no cut-and-dried universal definitions for any of those.
What often gets ignored in these discussions is the second half of “rock and roll.” And it’s not just us doing the ignoring; the music listening public proved equally indifferent to roll in its unadulterated form, initially preferring it mixed with rock and then eventually discarding it altogether.
Supposedly musicologists and a few underground groups have been rediscovering some of the chord progressions and rhythmic patterns of roll, but most of the recordings were lost.
Gotta be rock-roll music, if ya wanna dance with me.
Isn’t there kind of a contradiction there? If I gotta have that rock and roll music, but I can have it any old way I choose it, I should still be able to dance with you if I choose no rock and roll music at all.
IMHO there’s two separate questions. One is whether or not there’s a difference in style, and second is, assuming the answer to the first quesion is yes, what each style should be labeled. Clearly there’s a divide between the pop music of roughly 1955 to 1963 vs. that of 1963 through (the development of disco in the 70s?, MTVs start in 1980?, some other end date or none at all?). I’m not sure that attaching a specific label to the two different styles is all that helpful other than in clarifying what one is discussing in a discussion of pop music.
Also FWIW, I think metal is different enough from rock that it isn’t just another sub-genre.
Yes, but is “metal” distinct from “heavy metal”? 
And is death metal distinct than doom metal?
If you truly want to be depressed try listening to death plastic.
Death carbon fibers is pretty strong stuff, though.