I can see both sides of the discussion. On the one hand if you have a 20-22" screen then either of these two cards is overkill. 24" and especially a 30" monitor then both these cards come into their own and this is who the cards are targetted at. Alot more money is to be made by selling mid range cards as this is where the majority buy. Much better to sell 20 or 30 midrange cards than 1 or 2 top end ones (I don't know if thats the correct ratio, it would most likely be alot more).
However, both these cards are Flagship products. Products that advertise who is best. It's willy waving at the most extreme scale. At the moment that title goes to Nvidia, recently it was ATI and no doubt when the 5 series arrive ATI will reclaim that crown. This is great news for us, the consumer as competition is healthy.
Whether you 'need' these cards is pretty much irrelevant when it comes to enthusiasts. I mean who really needs 24gb of ram and a 4ghz top of the line cpu. Very few, if anyone actually needs that kind of power but it doesn't stop us all from WANTING.
I want a Maclaren F1. Do I need one? No but if I could afford one, it would be highest on my shopping list. Not so much for bragging rights (ok maybe it would be a little bit) but because 'it's the best'.