Sony has announced it will buy about 19% of Square shares, injecting some $124 million in the game developer and becoming the 2nd largest share-holder of the company.. Sony previously had no stake in Square. Square can still create games for other consoles, although from this quote that doesn't really seem to be likely at this point

"We are not necessarily obligated to Sony, because of this deal. But we can gauge the situation in the future and offer software to the best selling hardware maker, and at this time there is no doubt that Sony is the best,'' said Hisashi Suzuki, Square's president.

update Jack - This, by the way, is an absolutely huge deal. Square has made the most successful RPG's to date, and this almost certainly binds them to Sony for the forseeable future. There were rumors that Nintendo and Microsoft were in talks with with Square in order to get their games ported over. That seems to be a lost cause now though, and puts Microsoft and Nintendo at a huge disadvantage.