Can you just imagine if the Beatles, with their influence waning somewhat, started following the trends and made an album with Disco beats, or (*shudder*) they signed to Geffen and started making terrible synth-ey 80s albums...?
Just another reason that the Beatles were perfect, in the way that they walked out on a high note and left everyone wanting more. THAT'S how you do it.
Not to crap on the The Stones, but imagine how much more iconic their catalogue would be if they stopped, say, after 'Some Girls'?