I don't think it's that relevant to compare the elite of one era with the elite of another. Truth is that an uber talented 6-11 guy in 1968 was probably just as likely to play hoops in 2013.
The difference is the role players. Back then, every team had multiple guys who were just not that big and not that athletic. If you were 6'7 and pretty good at basketball but also pretty good at accounting, accounting was probably a better long-term career option. Almost nobody came from overseas to play. Every night a superstar could pretty reliably count on getting defended multiple times by somebody who was vastly inferior, akin to the difference being guarded by a high school vs college-level basketball player.
The huge salaries of the modern NBA put a competitive premium on those jobs.
On top of that, the pool of available talent grew exponentially bigger as the league became more popular, the US population doubled in size, and the international game grew in popularity (thanks in no small part to the original Dream Team). Bigger talent pool = more talent.
Plus, coaching, drafting, scouting, traveling, training--it all got much better as the financial stakes of putting out a good team got much, much higher. This all helped to make the average NBA player better (whereas I suspect the prodigy elite-types saw much less improvement. There's an upper limit to what anybody can do with a basketball.)
The superstars are still superstars. It's everybody else who got a lot better.
