Appleboy; I'm just a frugal sort. I usually only get a game ONCE unless the company gives me a good reason to buy it again.
Case in point; I'm getting 2.8 EVEN THOUGH I have DDD because of what comes with it (Not for DDD itself though). (I also bought FF3 twice, but that was because the DS version could not be 100%ed after they killed the internet support for the DS, so I bought the PC version when a certain raid in FFXIV gave me the itch to play it again) At this point, there's no good reason (extra content, etc) for me to buy Kingdom Hearts HD 1.5+2.5. I think some feel the same way. The only reason I'd buy it at this point is if my PS3 died, which I don't see it doing for years, if that.
And it's okay to want every version of the game though! That's you.
Tho yeah, I'm going to be excited to tell the friend, "No you don't have to buy a PS3 anymore for KH unless there's some PS3 games other than those collections that you want to play". She's going to love saving the money!