I don't think there's any doubt that 360 owners in North America are much more willing (and possibly able) to buy games than Wii owners have been up to this point, based on numbers alone.
Whether this means that Wii owners are all casuals or that 360 owners are all males in their early twenties who have the money to put toward a new game every 2 weeks is something for the analysts and the armchair message boarders to thrash out for themselves.
As far as SMG vs. Halo 3, it's going to take years for that battle to shake out. After 1 week, it's just impossible to tell. Look at Bioshock and Metroid Prime 3. Bioshock had a much larger week 1 sales (2x greater, I think?), but now MP3 is outselling it 2 to 1. At a differential of about 250K at this point, it is very possible that over the lifetime of the two titles, MP3 will eventually outsell BioShock.
SMG and Halo 3 could very well play out the same way.
Another thing you ignore is the fact that Nintendo titles will add a good 25% to their numbers from Japan (especially for RPG titles), which affects development significantly.
Also, as Wii hardware continues to outpace 360, the sales differential will diminish.
This "Week 1" mindset that people are bringing to this site from the way movies operate these days needs to be seriously reevaluated.
So say we all, yo.
