It would be misguided, I think, to try to define "high" and "low" by looking only at works of art themselves--i.e. things like "innovation" and such. "High" and "low" are first and foremost social terms, so they have to be defined primarily with reference to the people receiving and using the art, not to the the artworks themselves. This isn't really an answer to your question so much as a qualification of it, but "high" art is art which (for better or worse) is thought to confer some sort of elevated status to its audience, and "low" art is art that does not.
This has been the case in classical music for most of its history (though it's arguable whether it is still the case today), and even within its history different genres had different levels of cachet. Haydn, Mozart, and Schubert were not the first to write
Ländler by a long shot, but they were among the first to write them for elite audiences and not for the peasant cultures from which the dance was derived. That is why Hadyn, Mozart, and Schubert are canonical composers while the local village musicians of Moravia are not. Canons are instruments of cultural elites; that is virtually the definition of a canon. As you mentioned, the same system of status has been assimilated into pop music as well. Telling someone you were among the first people to be into the Sex Pistols gives you social credibility (in certain circles, anyway).
Again, none of this answers the question of
why this happened, or why it happens for some artists but not others; but it is a reminder that questions of "high" and "low" are as much about the receivers of art as they are about specific features of artworks themselves. Trying to find answers in the artworks themselves would only perpetuate the myth that there is some objective quality of value that inheres in them.
EDIT: As I was typing up this response, Coolwhip managed to sneak in and say it much more succinctly.