It's not a fair way to compare.
- The sales that the Wii had are the most important reason that all the Nintendo games made ridiculous numbers.
- 3ds & Wii U Smash came with no competition to both markets (3ds also beeing THE device in Japan).
- SFIV came in when fighting games were almost dead (mainstream). Also in a ridiculous time with Batman, ACII, CoD:MW2, Resident Evil 5, Uncharted 2, Bonderlands, Left 4 Dead 2, Dragon Age Origin.
- Don't think I have to say what happened with SFIII and the time it was.
- SF still sold 7M (according to Capcom) besides the fact that was bigger in the arcades
The problem with SF it's that it's not a party game like smash. I'm sure everybody has a friend that likes the game but doesn't buy it cuz "I suck at FG". Not saying it could surpass Smash in sales, but if it was as easy to play for casuals I'm sure it'll be much closer. Let's see how SFV does in the long term.