I had a thought when reading how Microsoft and Sony are both trying to mimic the Wii Remote and hopefully "its" success.
Honestly, I don't think it's the motion control itself that has made the Wii popular. As far as I'm concerned, the Wii has been a huge gimmick that doesn't seem to be improving much. It doesn't do anything (technically) that the other consoles couldn't do, but the reverse isn't the case.
The assumption seems to be that the "motion control" itself is what really made the Wii successful. However, without Wii Sports, it is highly doubtful that anyone would bat an eye at the Wii at all. Obviously, the Wii is flooded with piss-poor games, which barely deserve to be called "Games" on many occasions.
What Nintendo was able to do, is convince people that that Wii Remote would make everything "better" and "different". It's different, but a long debate could be made about the former part. Even staunch Wii supports have to admit, that the Wii controls are shaky most of the time. It doesn't react as expected, and even with a steady hand, it can be unpredictable. Sure, we could blame the developers, but in reality the tech just isn't consistent.
So they threw in a game anyone could relate to and play. Even if the Wii Remote had 20 buttons, it wouldn't matter if anyone could play it and it didn't look intimidating. It looks easy, and the concept matches obvious imagination. The mental Wii advertisement isn't Brawl, Metroid, or even Zelda. It's Wii Sports.
Look at Guitar Hero and Rock Band. They work on the same principle. The console doesn't matter. It really IS the game.
Sony proved that motion control alone isn't enough with their disappointing SIXAXIS controls. Often they inappropriately forced in games, and it shows. Motion control alone isn't as big of a piece of the puzzle when it comes down to it.
For MS and Sony to come in with motion controllers now just seems silly. They need to offer an inviting experience instead. If they insist on a new and simple controller, they better come out with several games that use it, and have the same type of appeal of Wii Sports or Guitar Hero for each. Hell, make four casual games that all come with the controller....so if you buy one of each you'll have the four controllers you need for multiplayer.
My bet is on futility with both companies if they aren't careful.