To be fair, there's a big difference between being able to run it on basic and to be able to have all of the options turned up. Oblivion especially is notorious for needing a TON of horsepower at the higher settings and resolutions, but most games will play on most things if you're prepared to knock down the graphic settings. For games like Civ (and drawing on my own experience, The Sims 3, since I helped out a lot of casual users with that), they'll play well enough so long as you've got a certain feature (pixel shader i think?) and 128/256Mb of RAM on your card, but the higher settings you go, the more detail you can have. For those on a budget, a £20 8400GS will run the Sims 3 just fine, and I expect that you'll see the same with Civ 5, especially as they've said they want it to be laptop capable, just obviously some of the gorgeous effects that we've seen in the screenshots will have to be turned off for that.
Some of the keener discussion though is aimed at the high end stuff - if you're going to put down £100+ on a peice of hardware, its reasonable to expect that you should be able to get 100% of the benefit out of the games you play on it! Thats where there's a little concern just now, wondering if the current first-gen DX11 cards will deal properly with the DX11 effects.