I really don't get it. Squenix is even releasing it as a digital download for the iPhone - why the hell haven't they put it on the PlayStation Store?

If you mean why isn't the PSP version on the store?  Then I don't know and I have to check to see if it's there.  If you're asking why the PSX version that you can play on your PS3 isn't on the store, I say you check again.

I mean the (vastly superior) PSP version.

Same reason Crisis Core isn't on there.  They're just slow getting their games on PSN, and it sounds like Kingdom Hearts: Birth by Sleep won't be on there for awhile yet either.

It's pretty odd considering Dissidia has been up there for quite awhile.

Square is just slow with things I guess.  And isn't Dissidia there because the Go was released here when Dissidia came out?