I don't know what you get at this price point that would be worth saving $75, and not just getting the D90. Just being able to use any lens on the D90 would seem to be enough to sway me to spend the extra money.
Yeah the naming convention is goofy -- the D60 (and the D40 before it) were the motorless little brothers of the D80. And before those, the D50 was the economy model to the D70. Now The little brother to the D90 is the... D5000? Guess they ran out of even multiples of 10 since everything from 40 on up was taken already, LOL.
I'd love to have a D90 but honestly the D80 is capable of way more than I get out of it, so I can't justify an upgrade.