I think it really depends on just how much collaboration occurred between sony/MS and Epic.
It's possible that they made modifications or considerations in their platform architecture to better support UE4 and thus Epic will probably not have UE4 ready for other platforms, specifically the Wii-U on launch.
At it's heart, UE is a multiplatform multi-purpose engine. UE3 ran on an iPad, it would be ludicrous to think that UE4 wouldn't in at least some form run on the WiiU. It's obvious the Wii-U is going to be vastly outclassed by those consoles in terms of tech, but I don't think we'll see a a wii->PS3/360 sized gap simply because that would result in the ps3/360 costing far too much money.
I think there might be some truth to it, but only initially.
If the PS4/360-next are really that much more powerful than the Wii-U, get ready to drop 599 USD again.