Agree totally with everything.. except for the single center focusing point ( I agree with that too... for you and me and John, etc...) but the OP's D90 won't do that... I checked the manual!
Looks like it is possible but is a function selection.
yes.. but if you look at the D90 manual pages I posted above... nowhere does it say Single Point and AF-C in the same areas.... but it does mention AF-C specifically for Dynamic area and 3D Tracking. My girlfriend no longer has her D90, so I can't test it personally any more. It is a bit ambiguous!
Unless Nikon is really screwy, shouldn't matter. They are two different selections. One for focus point/points and the other is focus mode. I could be wrong, as I am a Canon shooter for digital and Nikon shooter for film.