?

That's what they've been doing ever since the first Pokémon game. The difference between both versions is minimal.

Well it helped interaction between friends, because if I wanted everything, I would go to my bud and he will give me the ten Pokemon's that I am missing. 

And considering it will undersell each individual version, it's actually 3rd.

That aside, Pokemon as always has been the same game with different versions. Tracking them separately is like tracking Special Editions separately, except even worse because there are even fewer differences between Pokemon versions. Mind you, for once, Black & White are taking it a bit further by having different art styles between the versions and one unique city in each version.

Yeah I know that. But that doesn't explain why. 

RVDondaPC:  Nothing is different besides a few encounters.  They are basically the same game.

naznatips:  MHTri will have less content, and the online issue can be resolved through having a PS3 with Ad-Hoc Party or a computer capable of using X-Link Kai.  P3rd will recover some old monsters as well as the old weapons, that alone gives it more content.  It loses (possibly) 1-2 of the monsters Tri had because they are mostly underwater monsters (Gobul and Lagiacrus), but otherwise P3rd will have more content.

It's missing 4 of the 12 areas in MHTri (the underwater ones) and it isn't replacing them with any other areas that I know of, thus eliminating a lot of monsters and areas, and a lot of content. It's adding some new monsters, but it's a pretty big difference in gameplay content. The online through adhoc also won't have the matchmaking area you get online on Wii, and in general the underwater feature is one of the most interesting changes and major evolutions in this entry, so losing it makes it signifficantly less evolutionary.

well after capcom announced the release date for MHP3rd, sega delayed their game, Shining Hearts...lol