Seems kinda stupid if they didn't. Considering the Wii was all about "family fun", aka local co-op, hampering that with only one controller seems like a giant contradiction.
I'd like to remind you that the Wii is the Wii, and the WiiU is supposed to be a return to the roots and to the core gamer, mostly with Singleplayer or Online Multiplayer. Many would preffere "on the same couch" Multi to be concluded, hence the cries for having the option of connecting two, but with the target in mind, it's not a necessity.
It seems really stupid of them to make a console sold to the casual gamer and then make their next console completely alienate them. They are definitely aiming for a casual audience, if they didn't they'd have Gamecube level failures.
the are aimin to sell a console to people that play games a console for everyone unlike the ps3 or 360 or wii