While I agree with you in theory, there are plenty of reasons to stick to Nvidia or ATI for features not related to gaming.
Also if you purchase items based on a price/performance ratio, then going for an outdated card can sometimes be a good thing, as older technology can be much cheaper
Example: My 4890 cost me bugger all

However xevious, there is no reason in my opinion to avoid a 5xxx series if you are only using the card for gaming. a 5850, which you can get for a similar price to the GTX275 you showed in your original post, is MUCH quicker than a GTX275 in pretty much any game tested.