No, I think you’re definitely right. I took a few music history courses in college, and as far as I can tell, the last couple decades have seen a higher rate of change of musical genres than any other time in history. Gregorian Chant was sung with very little change over the course of centuries, and now we expect every decade to have its own unique sound. Granted, my courses mostly covered “classical” music, but from what little we did discuss of popular (ie, folk) music, it did not change at nearly the rate we’re used to today.
So, yes, I’m sure 50s audiences would be freaked out by a lot of modern music. And if you think the teenagers back then wouldn’t understand today’s music, just think what their parents would have thought of it!
But really, don’t most people have to go through their own type of evolution before they get to the more complex, hard-hitting music being made today? Maybe I’m wrong, but I don’t think that most people, when they first reach the age at which they’re trying to develop their own musical tastes (the pre-teen years, approximately?) jump straight into really crazy stuff. A lot of people that age start out by listening to bubble-gum pop, eventually outgrow it, then seek out something a bit harder, and on and on till you get to the cutting edge. For some people (myself included) this even takes a pretty linear form. I know I used to love listening to old 50s songs – doo-wop and the like. That kind of stuff, like modern “bubble-gum” pop, is very easily digestible. Eventually I moved on to the 60s, but nothing too “hippy” – early Beatles pop, but none of their “weird” stuff from Sgt Peppers; Beach Boys surfing songs, but not Pet Sounds. And on and on. I guess I’m kind of a slow study, because I’m 25 now and just breaking into the 90s – just got my first Dave Matthews Band CD, hey hey! Well, I’m not that slow, because I did take some great sidetrips – some jazz, blues, country, bluegrass, 30s-40s, stuff, etc. But rap is still mostly incomprehensible to me – at my current rate, I’ll break into it in a few years. 
Did most other people have to go through a similar evolution in taste, or were you able to jump straight from Disney sing-a-longs to Guns ‘n’ Roses?