That's a shame... so I take it the PS3/360 had none? The vids I saw must have been the wii version then, and yeah, it seemed pretty minimal and lackluster.
If the game lacked it already, I wouldn't expect them to develop it just for this release (this seems like a pure cash-in, like those "Game of the Year Editions" other titles get). Still, how hard would it be to just port the Wii version (even if it were basic)?
There is only so much modding can do, but if it were at least present, and modding was approved, it might be possible to tweak it into something worthwhile (but then if people don't take to the game in droves, then it won't happen, because the interest won't be there in the first place!). Since split screen gaming isn't that popular on the PC, I can see why they wouldn't bother.