I’m American and, more often than not, I have a hard time distinguishing an accent from English performers when they sing. They usually sound American to me. (Yes, I realize that many would argue it’s Americans who have the accent, but you get my drift.) I’m often surprised to learn that singers or bands I’ve heard for the first time turn out to be English. Adele sounds like she could’ve been raised in Ohio to me. Anyone else?
Many of the differences that comprise regional accents are swamped by the distortion that occurs when one sings. For example a major component of accents is vowel differences. When one sings vowels get stretched and changed to suit the timing of the song and this removes what might otherwise be the distinguishing features of one’s accent.
The consequence is that one tends to hear songs as being sung in one’s own accent. The actual singing leaves an accent vacuum that you fill with your own expectation.
I assume, then, it would be common for Steven Tyler to sound English to an Englishman?
Counterpoint: “a champagne supernover in the sky.” “I sawr a film today, oh boy.”
Weird exception: Billie Joe Armstrong’s accent.
Otherwise, American/Canadian/Irish accents are usually the generic singing voice.
It’s a choice from the singers’ side. Bands who work in a mainstream pop/rock style tend to take on a generic american accent, but listen to almost any band in a more british genre like punk/ska/madchester/indie/britpop/shoegaze and there is no mistaking where they come from. Like the Jam, the Specials, the Beat, the Stone Roses, Blur, Pulp, Ride, Belle and Sebastian and so on. For some reason these bands tend to not do as well across the pond though.
Singers incorporate their influences. You grow up listening to American blues and rock and roll, you sing like them. QED.
The question is whether you can inhabit that vocal. Watch a singing competition and you can see which decent singers still sound like they are trying to imitate their idols vs. those who are building their own thing. Their own thing likely brings their native accent a bit more to the surface, which influences their fans (e.g., Bille Joe Armstrong and his faux-UK accent, because he liked UK punk) and so it goes.
The standard pop voice is American-ish in style, usually miles away from the singer’s natural speech voice. It’s been creeping in since about the dance-band singers of the 1930s and 1940s, and particularly since the successive waves of different styles since rock’n’roll in the 1950s.
More important to me is whether or not they actually articulate enough for the words to be comprehensible, in amongst the orgasmic intakes of breath, the sobbing break and the wobbling warbles on any available open vowel.
Previous threads Why do British people lose their accent when they sing? - Factual Questions - Straight Dope Message Board
Why Do Many British Singers "Lose" The Accent When Singing? - Factual Questions - Straight Dope Message Board
My argument for why Standard American English really is "no accent" - - In My Humble Opinion - Straight Dope Message Board
So, then, it’s not just me.
Singing (in English) seems to filter out many accents. Klaus Meine of the Scorpions speaks with a fairly thick German accent, but when he sings there’s little or no trace of it.
It’s not automatic. It’s a stylistic choice.
Non-American blues & rock singers often try to sing in a sort of American accent. Rod Stewart comes to mind as someone who described himself as singing in an American accent, and being worried when he first came to America and had to do it in front of Americans.
Australian singers trying to make it internationally are known for putting on a “transatlantic” accent. One notable exception is Peter Garrett of Midnight Oil, who always kept his thick Aussie accent.
Yes, it’s a conscious choice.
Maybe they are used to listening to American singers and are trying to imitate them, maybe they think they sound cooler and more cosmopolitan, or maybe they just want to sell more albums in the US market, and think that’s the way to do it.
When this question comes up (I’ve seen it before on other forums as well) and someone says that singing automatically makes all singers sound American, I always wonder if they’ve never listened to the Beatles.
If you’ve ever been exposed to a variety of music other than contemporary popular commercial music, then it’s obvious that singers sing in all kinds of accents.
British classical or ‘serious’ music singers invariably sing in a posh upper-class English accent.
Scottish and Irish traditional folk songs are sung in heavy Scottish or Irish accents.
Sea shanties are usually sung in British working class accents.
Etc., etc.
From “Do You Want to Know a Secret”: You’ll never know how much I really curr.
Took me a long time to figure out that “curr” was George’s Liverpudlian pronunciation of “care.” 
Or The Proclaimers (“I’m Gonna Be,” etc.). Their Scottish accents are just as strong when singing as when speaking.
Funny, I’ve never noticed that word to have much of a distinct accent. Certainly doesn’t sound like “curr” to me.
That is what I’ve always thought.
Country singers sure don’t lose their accents when they sing!
I’ve always thought Eric Clapton is trying to sound like a Southern American Blues singer.
It’s always amazed me that anyone thought it was a good idea to let him sing.
My mom used to listen to Tom Jones in the early 70s, and so us kids were familiar with “It’s Not Unusual” and the rest of it. I remember being gobsmacked when I found out he was from Wales and had a thick accent.
Probably because he is. Those were some of his biggest influences.
That brings up a much bigger question though. If all of these foreigners can sing perfectly well in a normal accent, why can’t they just talk right all the time? There is obviously nothing wrong with them.