[philwelch]

Well, you'd have to go by the top n most popular songs for a given year, because otherwise you'll see an explosion over time since there were simply more albums recorded in 1980 than 1950, or in 2010 than in 1980. 2010 had a lot of shitty simplistic pop songs, but it probably had more prog-metal releases as well. Actually, if you go by all releases, pop music might have a diminishing impact, since it lacks a thriving independent scene.

Incidentally, the Beatles' influence is overstated--they usually popularized the innovations of others rather than innovating themselves. They were influential by virtue of their popularity, but they weren't as original. Pierro Scaruffi overstates his point perhaps, but has written the quintessential polemic against the myth of the Beatles: http://www.scaruffi.com/vol1/beatles.html