For me, part of it is (a) spoiler-related and (b) expectation -- can you reasonably expect, in general, that people who played the first central game might have played the second? Example: FFX and FFX-2 are on the same system; people who played X have a fairly good chance of being familiar with X-2. FFVII: OGC is in one format; its Compilation ingredients are in others (AC is a movie, there's that PSP game and that weird cell phone game and I just can't keep up with them but I hope I've explained it).

That being said, I actually do still think of X and X-2 as separate games, which is why I marked them as such in the poll. Probably because there was so much time in-between when I played them that I still mentally consider them separate entities.