This is a great factor. I don't even know what's on the PC's sheets. Oh I know the wizard is built around Magic Missile, and the War Priest's anti-undead power can Push 9, but mostly the players just tell me what happens and I roll with it. Awesome.
As a DM I appreciate the significantly lower prep time... and yet I can still create a stat block and mechanically reflect the race, class, template, theme and/or creature combination that I want. That rocks!
Several have mentioned the combats, but I'll go ahead and mention the improvisational tools. From the DC/Damage By Level table to the many "Improvising with [Skill]", I can run a D&D game with just one table and no minis if I want to.
I'm not sure how that differs from earlier editions, but. If you really feel that way, what you might try is running 1e/2e modules with 4e rules.It's the way that the published adventures are written that I don't like. Even the better ones (The Slaying Stone, Reavers of Harkenwold) make it very easy for the game to play out as a series of mostly-unavoidable combat encounters with short breaks for role-playing and exploration.