1) it's controllers are awesome. they're wireless and don't weigh a ton, like the wireless 360 controllers. If you don't think so, fine, but 13 million people disagree.
They're still not as good for playing games with real controls and almost all Wii games make terrible use of the Wii controller features. Most decent Wii games would play better on a Gamecube pad.
Most things that are popular are crap that cater to the lowest common denominator, so popularity doesn't make the Wii controllers better(
and I don't think that their are 13 million more Wiis than 360's sold).
2) Better online strategy. YA RLY. It's a commonly known fact that the internet is made of a series of tubes, but did you know that these tubes are an infinite douche recycling system? Any online game is going to be filled with these douches. You can block/blacklist them all you want, but the internet will always make more.
For Smash Bros, (and online DS games, incidentally) it works on a whitelist system; only people you know can play with you. all the a$$holes are filtered out with no effort on your part. If one of your friends turns out to be an ass, you can remove them. It's pure genius.
EGM had a feature recently, where they asked fans of non-Halo FPS's how their game better is than Halo 3. More than one game's players gave the excuse that because its so unpopular, they don't encounter as many a$$holes. Its kinda like arguing that the TG-16 was better than the Genesis and SNES because you couldn't find the hardware or games for sale in very many stores and when you did, you didn't have to fight anyone for the last copy.
But the "genius" a$$hole filtering system of Wii games is actually an extremely crude version of Xbox Live's Friends list. Most online games allow you to play with who you want, in custom games and other ways
as well as matchmaking.
3) it's not overloaded with FPSes. if you like that genre, fine, the 360 is the system for you. but I don't, and it seems like every other game for the 360 is an FPS.
The 360 has the most variety of games of the 'current' generation. Everyone knows that the Wii is drowning in gimmicky garbage that Nintendo should be ashamed of granting licenses for in the first place. Other than waggle games, is their any other genre that the 360 doesn't crush the Wii(
other than maybe platformers)?
The PC Engine may be overloaded with shooters, but that doesn't mean that it doesn't have a ton of other types of games too.
4) good first party titles. I have yet to regret purchasing a game made by Nintendo for the Wii. I can't even name a Microsoft 1st party title. If that makes me a Nintendo fanboy, so be it.
Unfortunately, their are only a handful of decent first party Wii games. You could argue that the top tier 360 exclusive titles don't
greatly out number the Wii's(
although Dave Halverson says the Wii only has 4), but it also has a bunch more quality titles that are exclusive to the 360/PS3.
And then their are still all the advantages that the Xbox 360 has over the Wii... but it doesn't really matter since people should just buy the console with the most games they want to play. Around here, it seems that most people would rather play Turbo/PCE games than any of the current gen consoles.