"One of the reasons I moved away from Nvidia was the whole flogging a dead horse 8800 mid-range series debacle. Same re-branded chip held them over for three generations iirc."
4, actually: 8800GTX, (PCIe 2.0)9800GTX, (die shrink)9800GTX+, and (no change) GTS250.
The big reason they would do this would be so they wouldn't have to spend the engineering resources for a total redesign. It certainly is not "to try to fool your avg person into thinking it's a newer card when in fact all it is are extra last gen gpu dies that these companies have that they need to find away to get rid of." Granted, it can be annoying for users at times, (I'm a GTX680 owner, and I can't SLI to a GTX770) but it does help keep costs down, and that keeps prices down.