When nvidia did it, and then did it again, they set the precedent. AMD is simply playing the game by the same rules as nvidia. It's sad that AMD couldn't be better than this, but it is a highly competitive business and you can't afford to ignore your enemies tactics.
I thought it was a good move, in principle, for Nvidia to do it with the GTS 250. It saved them some engineering resources. The GTS 250 (9800GTX+) performed as you would have expected a part just below the GTX 260 to perform. It correspondingly used less power than the GTX 260. Its feature set was pretty much the same. And of course price was lower. The only shady part is they did allow companies to literally replace the sticker on the 512MB card, while the 1GB got a new, more efficient PCB design.
What was shady about the 9800GT is that some 65nm chips were sold under the 9800 brand which included 55nm chips. I think 55nm should have been standard and enforced. The first 9800GTX was different enough from the 8800GTX to warrant a new name. A new generation? Well...
AMD set a precedent with the HD 3870, because the HD 2000 series were so horrible they had to get move on from that brand of series. But when you bought a 3870 you absolutely knew you weren't getting an HD 2900; there were no straight up sticker swaps. That wasn't always the case with the 9800GT and GTS 250.
Before the 3870/9800GTX, the companies would have called these cards the HD 2950 XT and 8850 GTX.