I would certainly agree that there is nothing inherently more or less RP about D&D 4th Edition. There might even be more in there than the first edition books. I don't remember the 1st edition books going into much detail about how to role play, but I could just pull the PHB off the shelf at home and take a look to refresh my memory.
I will say that D&D (in general) has less of an RP bent than many other systems out there. Pendragon, the World of Darkeness books, and most of the rules light systems (such as BESM) all have a much larger focus on RP than D&D does. Nothing wrong with that of course (and some of those games might not be the kind of RP you like anyway) but they certainly put greater emphasis on it than D&D does.
However, there is nothing in D&D that says you can't focus on RP, it's just that the mechanics and source material do not support your efforts as much as other systems do. So it then falls on the GM/DM and players to promote it. Which I think is actually a good thing, because I know a lot of people who would have been turned off by the RP expectations of say, WoD if they had not been eased into the hobby with D&D.
Now of course I have had the rust blown off with a few months of running a D&D4e campaign and I'm ready to move back into a character driven rules light or rules medium game, and I think so are my players. I've been getting some complaints about the endless hack and slash progression of the current module we are running, so I am starting to take liberties with the module in order to juice up the RP a little. (I’d advise against buying the “Scepter Tower of Spellguard” module, it’s just a series of hack and slash encounters once the players get underground. While they’re above ground there are some RP opportunities, but the module provides little support in that regard. My players are thoroughly sick of it and we aren’t more than half way through with it.)