If it weren't for the flop of The Wonderful 101, I would have thought Bayonetta 2 would do decently. However, it seems like there's a good chance that Bayonetta 2 will "flop" regardless of how good it is.
Why people are saying "X" I don't know. Simply saying about its genre and the Wii U's userbase doesn't really explain it because for X to be a "flop" it would have to sell very little. A title like X, I presume, would have expectations to sell around 1m. A flop isn't just a failure, but a big one. Less than 500k is most likely going to be the "flop" area for the game, and there really isn't much to say that X is going to be a flop.
As for Smash Bros for Wii U, I can see why people think it will flop, but I personally think it wont flop. There are a large number of Smash Bros fans who want the Wii U version specifically. If they are indeed the representative group of Smash Bros buyers, the Wii U version may even outsell the 3DS one.
Of course it is all speculation, but I still think it's weird people are constantly saying those three games as the flops.
I can see why people will say Hyrule Warriors, but I think no one is really expecting that game to do amazingly.
edit: I mean I think it's weird that more people are focused on the Wii U than anything for flops. Expectations for software sales on Wii U aren't that high right now to begin with.
