3rd parties, the key to Nintendo's success on the U

[happydolphin]

Seece said:
Rayman Origins didn't do much if any better than PS360 on Wii, so I don't think Legends would have.

If a game isn't exclusive, it's easy to conclude that's the reason it sold relatively less, not much more or on par.

Here's a counter-example from the 3DS, a timed exclusive:

Pos	Game	Platform	Year	Genre	Publisher	North America	Europe	Japan	Rest of World	Global
1	Resident Evil: Revelations	3DS	2012	Action	Capcom	0.23	0.15	0.30	0.04	0.72
2	Resident Evil: Revelations	PS3	2013	Action	Capcom	0.03	0.06	0.15	0.02	0.26
3	Resident Evil: Revelations	X360	2013	Action	Capcom	0.03	0.03	0.01	0.01	0.07
4	Resident Evil: Revelations	WiiU	2013	Action	Capcom	0.01	0.01	0.01	0.00	0.04
5	Resident Evil: Revelations	PC	2013	Action	Capcom	0.00	0.01	0.00	0.00	0.01

There are others that show that a game can sell a lot better if/when exclusive than when it is a multiplat.

I think what you're trying to say is "why should devs make exclusives when they can make more money making them multiplat". The main reason is that the market on the twins is saturated. A developer could build its own market in the span of a generation or two on Nintendo platforms and have the chance of making Nintendo-like sales on the long-run, if they can pull it off.