Perhaps, but three points:
1) If they don't research their purchase, I don't care what they buy.
2) It will matter only if they pay more for a 6770 than a 5770. If they are the same price (on average, given differences between vendors) or the 5770 is EOL'd and not available for purchase, then the point is moot.
3) Further question: Why do you personally care what a casual buyer does? What is your personal investment in their purchasing decisions?
You have a point and really all consumers should do their research. Though how many of them go to someone whom knows rather than go and do it themselves? I'll expect more ask a friend, or someone they know, than do it themselves.
It can be hard sometimes to argue with someone that it's the same card, that they shouldn't expect faster performance and in the case of the 8800GT and 9800GT a minute slower performance.
It was shoddy marketing when nVIDIA did it, and it is the same when AMD does it, and I won't change my stance just cause it's now AMD. Will it stop me from purchasing either though? No.
It's already confusing for some people, and then when a product is rebadged it doesn't make it easier. Admittedly AMD haven't hidden it (unlike nVIDIA), it's in the same price range (unlike nVIDIA) and does add some features (like nVIDIA) but it's still a rebadge.
I agree that if the 5770 is totally taken off the market, then the 6770 sits nicely where it should and that there would be less of an issue once that happens
It's not the end of the world, and yes, it is being taken too far from the bulletin that it should be. As long as people now know and it's in the same price bracket there is nothing more to say about it.