Most people who buys lots of Beatles records maybe don't listen to the stuff carefully in the sense that one might listen carefully to Elliot Carter, but they know there's something exciting going on that separates the Beatles from, say, the Monkees or Sonic Youth or Steely Dan. I don't think generational means squat. I think what we're talking about here is power. Not is the distorted loud guitar sense or the Elvin Jones sense, but something more elemental.
I'm not sure why you selected to compare the Beatles to the Monkees, Sonic Youth, and Steely Dan as these are very disparate groups, both stylistically and artistically. I'm not sure what you were getting at by comparing Sonic Youth and the Monkees, so I will refrain from taking any offense. I do agree with your statement about power; there is certainly something ineffably effecting about the Beatles or the Beach Boys at their best. It goes somewhere beyond virtuosic chops or the extent to which it is groundbreaking--or even possessing good melodies. Zach