When talking about, "playing D&D," I tend to be quite inclusive, particularly if I'm talking to someone who is not that familiar with role-playing games in general, or to whom I am only talking in passing (making small talk, or whatever).
I'll say, "I'm going to be playing D&D this weekend." if I'm going to be doing basically any sort of role-playing, whether that's the actual D&D game, or when its Iron Heroes or RIFTS or HOL. Mostly I do this because saying, "I'm going to be playing HOL, this weekend." inevitably gets a, "What's that?" to which I have to respond, "It's like D&D, only on crack." So... saying, "D&D" rather than "HOL" (or some other variant on the lesser known rpg title) is just that much easier.
I wouldn't say that I'm going to be playing D&D if I were playing, for instance, HALO or Hockey, Texas Hold 'em, or something like that...
Later
silver