Yeah I know about that video, and as Microsoft said, that's pretty damn accessible to anyone :D.
However, that's microsofts first load of software, it's going to be deliberately dumbed down and light hearted. It's a software issue, not a hardware one.
Onto hand/fingers, I have to agree, to have this degree of accuracy would have been wonderful, but I could also see it causing a lot of issues (when jumping around do you know if you are making a fist or not? How exactly your fingers are moving?), but still, you're correct. I do wonder if it is capable of detecting a fist from open palm though, I would guess (from the night vision vid) it probably should be able to, maybe not so easily for small children, but certainly for adults.
But then, what exactly do you need fingers and precise hand movements for? Interacting with objects is often done with a single button now, so that's easily enough replicated by placing your hand over the object and pushing/pressing forward. Any shooting could easily be done with a light gun (I really really really hope they do this). Movement has a number of possible methods, as to which will end up being used will probably depend on reviews and comments as developers try them out, anything from one hand being a joystick, to the movement method used in the super mario hack.
Racing games in general are perhaps not going to be the best genre, and it may, or may not work well with RTS's it depends on how accurate the positioning can be (though voice commands could easily be used to select units, and give orders, though directions would be better with a more direct interface). Basically using voice to replace the key holds to tell the unit to patrol/guard/hide etc.
Obviously it depends on developers, but I would hope with this big user base, developers will go for some more mainstream games for your typical gamer.