Classic Rock will always exist, it is living on through many modern bands who are recreating the sound. The Answer are a good example of this. Of course, it will have a modern twist to it, but you can still replicate a specific sound to exaclty how it would have sounded during its peak if you wished, since many influences and methods of approach make the difference between. But when it comes to success...
The music industry has definatley changed, many new avenues and equimpents are being explored. For success in the charts sake, bands will use simplistic and catchy songs compared to the other material off their albums which wouldnt necessarily do well in the charts. But that doesn't mean ALL their music is like this. Many times I have wished for bands to release certain songs because they are great examples of what they can do, yet the less colourful tracks end up getting released after their golden first and second releases die out.
The thing I find is that Classic Rock and modern rock arent a million miles away from each other. Bands are still using the same techniques as the old classics, just in a different modern way and are earning money. And I see nothing wrong with that, since it is a profession after all. And once bands have established themselves, they dont need to prove anything so as a result tone down their rebel like ruthless attitude, so they can sink into their own nicheand just enjoy themselves. I don't see what is so wrong about this. That's why to me the words 'sell out' are pretty bland. So in my opinion it is preference of the sound, artist and sometimes the characters behind the music that a liking/disliking is based on. Oh, that and their appearance. With this comes the consideration whether something is classic or not. Contrary to opinion, of course.
No matter what 'genre' a song may be, if it has a catchy melody and interesting direction, I'll listen to it. There's a lot to be learned from every piece of music out there no matter how much you may or may not like it.