The 20-50 million dollar budgets that Reggie is stating sounds about right. Have you seen how much bigger game teams are getting? A team of 50 people is around 4-5 million a year in just salaries and benefits (I'm averaging out salaries here to around 70k a head - see Gamasutra's salary survey for more specifics - and estimating about another 12k a head for benefits but this can go a lot higher depending on what a company will pay for).
Then there's publisher support for marketing, sales, QA, etc - the people actively working on a project will be billing to that budget. That's probably another 2-3 mil a year. So in terms of just headcount, in 2 years you already hit the 10 million mark.
Throw in equipment costs for PCs, general IT support, developer equipment, and vendor support. We haven't even touched on overhead for paying the basic stuff like rent for the office a dev team is leasing or the electric bill and what not. 20+ million dollar budgets shouldn't be that surprising. Which is why companies want to release these high-budget games over multiple platforms - it can increase costs by quite a bit, but you're more likely to at least break even as you have a bigger userbase to try and cover sales.
So for a Wii developed game to cost between 5 - 10 million, you'd have to have a team size below 25 people, a development schedule less than 2 years, and not go totally crazy on marketing costs. You can probably get away with this on the other platforms as well, but you'll have much higher development costs due to the difference in equipment cost.