If I was SE, I would delay FF XIII until holidays '09 when the PS3 will have a bigger base. The fact it isn't selling isn't SE problem, it's Sony. SE will only care that they can sell enough to be profitable, preferably highly profitable. By Holidays '09 the PS3 will be cheaper, possibly much cheaper and have a bigger install base. That's good for SE.
As for KHIII this has been debated to death but in all likelihood it'll be Wii exclusive as that makes the most sense. Wii has - bigger base, especially in Japan, a more Disney friendly audience, cheaper development cost. You only have to look at how much better Sonic, Lego and other cartoonish games sell better on Wii than PS3 to see it's pretty much a no brainer, it'd sell LOADS more on Wii. As for making it on both? Why? Unless PS3 owners would be happy with an enhanced Wii port. It won't be the HD game you'd want.