SotC sold very well. It deserves a lot more, of course, but it broke a million easily, plus it improved a lot on ICO's figures (700.000 worldwide, which isn't bad by any means).
And Sony knows that they give the company a very good image, and they might become system sellers for some people (not as many as GT, of course), plus if they are profitable (even if they are not huge money-making machines as GT) and become a leveraging option for people in choosing the PS3, Sony will continue to support them.
And of course, adding a guaranteed triple-A exclusive to the lineup isn't something Sony would want to avoid. After all, Team ICO is the best developer Sony has...and they will be one of the things that will make me get a PS3 in the future.








