The divide seems to be coming from a misunderstanding of the medium itself. C&C, non-linearity, roleplaying (as in choosing story and combat options without stats), affecting the story, etc. can be in every game ever due to the interactive nature of video games, while roleplaying based on stats can't be. Think Fallout and AoD. Basically, to qualify as an RPG, it has to fulfill some of these criteria -
1. Stats affecting your character's ability to influence the game world in and out of combat (Fallout, AoD). This is the crux of the matter and many RPGs don't get this right. This is where the "role" in "role-playing" comes into play. If you aren't playing a character with inherent strengths and weaknesses (represented by the stats) then there can't really be any "role"-playing, can there? You are playing yourself. This is also where the term RPG kind of portrays itself as inadequate because of -
2. "UI-driven" combat. That means combat should be controlled through the UI and not through your direct keyboard and mouse input, i.e. no "left-click for fast attack, right-click for heavy attack", you know the drill. The most common form of RPG. Think IE games and most blobbers.
3. You are playing defined individuals (or an individual), so no masses of faceless mooks like RTSes.
4. "Indirect movement", as in your character can only interpret movement commands, rather than pressing CTRL to dodge or something like that. First-person blobbers don't have dodging in that sense or movement outside of directions on the map, but it's much more intuitive to directly control those directions, and they fulfill the second and third criteria.
The term is much more rigid than people think and I think it's strengthened by having a concrete framework, especially on a forum for RPGs.
What's more RPG, Diablo or New Vegas?
Diablo. New Vegas is an FPS.