SD card query with D7000

I've been using a D90 for the last few years but recently I helped myself to a D7000. Now with the move from 12MP to 16MP I was expecting to see a 30% increase in the need for storage of the RAW files but the two cameras seem to behave completely differently.

If I put a freshly formatted 8GB SD card into the D90 it tells me there is room for 528 pictures on the card. If I put the same card into the D7000 it tells me there is room for 218. That's considerably less than half the number that the D90 would give - for just an extra 4MP. What is going on?

Both cameras are set to RAW only. The D7000 is set to use the SD slots as 1->2 (i.e. fill up 1 then move to 2) but there is no card in 2 anyway.

Is there some strange setting deep in the menu which doubles the size of the D7000 RAW images or something? It doesn't seem right though.