or maybe 8800 gts 512 to 9800 gtx to 9800 gtx + to 9800gtxwtf +++
It's nothing like those. They were scheduled refreshes/renames which went along fine and were more to make up for a complete lack of a new mid range product than due to any delays.
Things like X1800 -> X1900 were product refreshes which came quickly (4 months) due to a delay in the initial product, and no delay in the refresh.
Refreshing a product as normal isn't the same.
The 5800 -> 5900 would be another comparable situation.
The main difference is that (we assume) Fermi will perform well, whereas traditionally delayed products that get quickly refreshed don't perform up to snuff.
Nothing particularly unusual about seeing a delayed product get replaced fairly swiftly, both companies have done it before.