Hussar
Legend
3e and 4e (4e to a greater extent) make it possible to play D&D with a very high percentage of session time devoted to combat - 60%, 70%, 80%. You couldn't do that in 1e and 2e, at least not with non-casters, because for non-casters combat was so uninteresting.
So d20 makes a new style of gameplay possible. Ofc you could still play it with much less combat, but you're no longer forced to by the system. In that sense one could say 4e encourages combat.
Umm, what?
Considering that the first decade or so of D&D was pretty much nothing but dungeon crawls and killing stuff, I think you're playing pretty fast and loose with your definitions there.
Heck, expanding what I said, OD&D, and Basic D&D did not reward roleplay in any form. There are no rules that reward any roleplay in there at all.
Looking at the old Dragon magazine articles, you'll see examples of campaigns where people had gone through literally dozens and dozens of characters. The idea that older versions of D&D were more heavily invested in role play certainly is a very strange claim.