I'll give you an easy way to tell. Look at Dell's profits. take 10% of that. That's what Dell makes on the over-$999 market. Again, if you look at Apple's PC profits, take 90% of that, and you get Apple's profits. That should give you a (rough) fuller picture of how important that 90% is.
Except for one thing. It's damn near impossible to find a PC that costs over $999. Most Dell's/HP's/Toshiba's, etc, from Best Buy are sub-1000, with better than MacBook Pro specs. Heck, I bought a Dell WITH a 2-year, on-site warranty with better-than-Macbook Pro specs, for less than $999.
10% is basically a rounding error, and if you approach it that way, you should be able to see just how much Appple p0wns - not the over$999 market - but the consumer in general.