I don't get it, Take Two says that the delay between GTAIV and the episodes caused lackluster sales, but they "are proud to finally deliver" them to the PS3? Good luck on this one guys, I'm sure another six months or whatever its been is just what they needed.

The episodes are completely developed, MS paid Take Two for keeping them exclusive a certain time, why shouldn't they port them now, that this time seems over, to the PS3 and the PC? The porting costs will be minimal, it would be a strange idea not to port them.
Even, if they don't sell like hotcakes, Take Two will make profit with them. The question is, will a GTA V be able to get GTA IV numbers, or is the time for GTA's reign over?

I can only speculate but my understanding is that the PS3 is hard to develop and program for. My impression is that would include porting a game from the 360. If Rockstar has been readying the expansions from the original time of the release and they had already invested the money, this makes sense, but if they had an opportunity to evaluate the expansions' sales on the 360 and after that greenlit the expenditure I don't get it, except as fanservice to PS3 owners who don't also own a 360.

The game is already ported to the PS3, the game is GTA IV, the DLC content runs completely on the technology of the original game, so everything, that has to be done is adding the new content to the old game. So I don't think there were much investements necessary. I am pretty sure, all 3 versions of GTA IV were shipped with an identical internal structure, that made it possible to expand the main game with Rockstars expansion packs.