I don't think there was ever a need for this card, however, it IS an advancement of technology (as it's done on a 40nm process), and that is plenty to bring it out. It doesn't bring any higher performance, just (likely) more performance per watt, more performance per dollar (well... a little, maybe), and something for ATI to work on their 40nm process with.
So really, it's just a card they made to test the 40nm process, increase yields on what may have sold very well (HD 4830's and 50's), and maybe make a buck in the process.
So... the positioning of the card seems good to me, especially since it'll likely use less power than the HD 4850, and its price seems to be pretty well in line.