Here's an inherent problem with D&D with 3.x and most likely with 4e as well. The game tries to emulate everything you can possibly do. While this is nice from a play balance point of view, being able to make rolls for just about every situation or challenge means it's easier to do so, and thus, people are more likely to do so.
For example, with the interaction skills, such as Bluff and Diplomacy in 3.x, it's far easier to just make a roll than to roleplay it out. Not only that, even if you do roleplay it out, some DMs make you roll anyway, so what's the point of doing the roleplaying? Some DMs will give a bonus to an interaction roll for good roleplaying, and that's a good middle ground.
You can roleplay out of combat and you can even roleplay IN combat! But you aren't forced to roleplay, and I think that's a good thing. Some people are better at the whole roleplaying part of the game, and I'm not sure it's a good idea to require something in which some players have an inherent advantage over others.
There's nothing in the rules that prevents you from roleplaying your character through every situation, combat or not. However, there's also nothing requiring you to roleplay. Add to that the fact that the vast majority of abilities that exist in the same are for the expressed purpose of engaging in combat. I think that's why people sometimes want to contravert combat with roleplaying (and vice versa).
One thing that can help encourage roleplaying is to change the XP reward model. Switching from a strictly kill based XP system to a more task/accomplishment based XP system, while adding optional components for ad-hoc roleplaying awards, I think that would be something you could do in the rules to encourage more roleplaying without strictly requiring it.