I'd imagine that Sony balances return vs investment for this. Right now, on the evidence, there is a far better return - not just in revenue but in terms of meeting tactical and strategic goals - in investing their 1st party on titles for US/EMEAA rather than Japan.
Part of this equation I would imagine is current sales. For home consoles in the region PS3 seems to be selling fine in terms of what's possible. Looking at PS3, Wii and 360 it's hard to imagine a lot of effort would actually result in many more console - or even software - sales.
So I'd say they're actually thinking about where the demand is and what the return is.
I also suspect the figure they'll get enough 3rd party now to cover the difference.