NSMB Wii sold way more than either Galaxy game. Just because Galaxy 1+2 are regarded as the better games doesn't mean the general public knows that. Wii Sports was nothing but a glorified tech-demo/mini-game compilation, but it worked.
The Wii U launch backfired for a couple reasons. These include not separating the Wii U from the Wii, proper third party support (why anyone thought people would buy old ports or games being released on PS3/X360 is beyond me), and a lack of first party support. They thought could ride the Wii U into instant victory with NSMBU, NintendoLand, and a bunch of old ports/titles being released on existing consoles. The system was doomed to have a subpar launch and that's why it isn't selling. Fortunately it looks like they'll recover. The Wii U is a next generation console and Nintendo is responsible for bring asymmetrical gameplay to consoles. Looking back at this E3 it's pretty clear that Sony, Microsoft, and especially Ubi have jumped onto that bandwagon.
NSMBW sold a lot, but it DOES NOT SELL SYSTEMS. Games like NSMBW are great games that people will eventually get, must-haves... not system sellers. There's a difference. Wii Sports clearly showed off what the console was about and it came for free with every Wii outside of Japan. The Galaxy games had a 'wow' factor that made people want one. Galaxy 1 most certainly helped push systems early on.
People don't buy a Wii U for NSMBU... they buy a Wii U, then get NSMBU. Most Nintendo fans that got a Wii U, got one because they know there's a lot of awesome games coming, although there's also some that got it for things they currently think are awesome (like Zombi U). Anyway, the Wii U would've sold if it was a €250 system with Nintendo Land as a pack in. Or hell, maybe even $200 with the worse economy these days. Instead a Wii U cost €350, that's too expensive for that crowd. At a price point of €350, their target audience should be Nintendo fans who want typical, incredibly polished, adventurous Nintendo titles.
Really, Nintendo Land was released 2 years too early.
Read the mania: http://www.fanfiction.net/~nonexistinghero In SA2, it's Super Sonic and Hyper Shadow.