I think "the classic greats" introduced music in a way that just isn't possible anymore.
The Stones and Beatles basically recreated the American Blues and presented it to a white audience that wasn't familiar. The prog greats combined rock n roll with classical and theatrical themes (more math-based, more time changes, etc). Neither genre was more innovative than some of today's groups, just that they had found something new to present.
With the internet, there's very little "unfamiliar" left for modern musicians to introduce.
Not to say they weren't amazing, just that it was more than their talent. IMHO.
Oh, and also the popular music industry hadn't yet been shaped into this cookie-cutter throwaway cycle that we're currently in. Record companies used to sometimes develop artists, whereas no there's no chance to grow - "have your single ready for distribution and competition with the million-selling artists, or you're gone immediately."