I think there's at attitude and an aptitude that exists now that in order to play great defense, you have to be a poor offensive team. Or, rather that great offensive teams cannot play great defense.
The thing is, I recall the Lakers/Celts of the 80's - both teams were fantastic offensive machines and were able to play great D.
Maybe what we're seeing now is a lack of imagination, and the results of a watered-down league. I don't think we'll ever see lineups so stacked with talent as those teams were again.