Yeah, you're dead right.
I sank over 100 hours into MH3 on Wii in single-player, and I haven't started yet a 5 stars mission, so I gather I'm still missing out on the best missions.
The game is quite demanding but also extremely rewarding, the sensation when you fell a giant monster after almost an hour long fight is exhilarating, maybe this is partly due to the fact that monsters do not have a life bar.
That being said, it is true that I crave to play Monster Hunter 3 Ultimate, but if that was not enough, there are also other interesting games to further justify the purchase of a Wii U.