I'm not sure why it is that people seem to forget that one 280 handily beats by 40% (in some tests) 2, that is *2* last generation top cards.
more than double with what is invariably extremely early beta drivers for a whole new architecture.
I think there's something broken with your expectations.
In any case so long as one card doesn't completely kill the other, its all just a question of prices.. personally I tend to believe that one 280 costs less to make than 2 4870s, and ATI will still have to sell at a lower price than the 280 because frankly if they don't pull out of the mud in this round the company may well go down the toilet... so...
Well, here's to low low prices on great hardware!