Advertising an older game is more cost effective for Nintendo than it is for a 3rd party publisher. Nintendo is the console maker, publisher and developer of their game so they get to keep the approx. $30 a publisher would take in. Plus the commercial also advertises the Wii or DS. A 3rd party publisher will still take in the same $30 but they will need to pay Nintendo a licensing fee and a royalty fee to the developers. So their return on each additional copy of software sold due to advertising will be a lot less than Nintendo's cut.
Thats pretty much what I was saying :/.
Third parties work-around seems to be getting games with well known brand names, they don't need advertising as any Joe Public knows what Star Wars or Resident Evil is, and I'd guess alot of the Wii audience just buy games as 'shelf' purchases. They don't follow the internet hype, look at the metacritic score and debate the best possible release that month, they go in the shop and see what takes their eye. The only added expense for a publisher then is buying the best store spaces - and maybe license fees.
This year I think the biggest third party Wii hits are going to be licensed software, or stuff with some sort of brand name. It gets around the whole advertising issue, makes your software stand out etc.
The other thing we'll see is big money spent on trying to establish these brands - we're guranteed to see another de Blob, Boom Blox, Shaun White's etc because the money spent marketing them will be expected to not be needed for the sequel. I look forward to seeing what EA do with their Fitness game.