Publishers are constantly running samples, taking polls, measuring demographics, etc...but even without that, you need to look at 2 factors here.
1. The genre. The single largest draw to buying a FPS is online multiplayer. You don't need a single test to verifty this at all. Just look at the sales and trends. It's all there for you.
2. Time constraints. The X360 being the lead development platform for the title means that Wii iteration doesn't get time to add in "extras". It gets what they can cram and then we're lucky to even get that in working order. Given this, they have to choose the features that will best attract gamers to the Wii iteration. And that means sacrificing one of those big features. Local multiplayer is far quicker to get axed because of bullet 1 above and because the game engine is already deisnged to run online multiplayer on Wii and it's not designed to run local multiplayer on Wii. So you'd need major engine modifications (again) just to get a feature added while also sacrificng a feature that is a larger draw anyway.
The rEVOLution is not being televised
