When it comes to sell a product, it all comes down to how people perceive it. In that case, I agree with you, but had they come with a hand drawn art-style for example, people would have see it as a new Mario I think...
IMO they really thought that people would be happy to come back to NSMB art style and music. This is REALLY poor marketing and a gross misinterpretation of what the market want with the release of a brand new console. besides, it just confuses people with the Wii. Add to this the release 3 months before of NSMB2.
NSMBU may be great, but it is really poor (and lazy) marketing. It is a very good example to show how the suits making these decisions by Nintendo can sometimes be out of touch with people's expectations (Miyamoto's "really, you want a new F-zero?" is another example if it is not just trolling).