I think it just boils down to the fact that numbers are showing that the Japanese game market is shrinking and they seem to just be running around like a chicken with it's head cut off looking for some way into the larger western market. As much as some of Squenix's games can make, they also are huge and expensive to make, just look at how long FF XII is taking. Perhaps this is a way to leverage that with shorter games that cost less to produce and have shorter turn around times. All in all though, like Koyota says it is not because Eidos is a great choics (It's not, we can all think of better ones.) but the only one they can probably afford. Taito it ain't.

Eidos' European distribution channels will also give Square Enix a greater immediate presence over there, and now Eidos has a huge partner in Japan. This really seems like win/win from all sides.

Seriously though, Square-Enix IMO got kinda lost in the last few years and Final Fantasy is a wreck now and all… But I want them to keep being mostly a RPG company; and buying Eidos/Tecmo is not exactly my notion of that, hence I rather see then focusing on them, Bethesda would be a good purchase for them, for instance (this said I HATE bethesda games, but… would make more sense than eidos anyway)

It's more likely that they'll set Tetsuya Nomura on redesigning Lara Croft for Eidos's next attempt at Tomb Raider “revival.” Then again, if he can make her look more…normal…I'm all for it.