While I can't recall a single instance of nVidia using 360/380 publicly this is what they were referred to - and I assume the name nVidia gave - by several companies, journalists, etc. who have actually dealt with the cards.
AS you said, I think it was a 380/360gtx for a long time, last gen cards were the 280/260gtx, unless you change the name completely to a new scheme. So calling them a Giraffe 90 and Zebra 80, then the basic naming convention would be to move it up a generation to a 380/360.
I really think its a case of making the decision to move their low end to 3xx cards so they can have an entire 3xx series range available at some point throughout 2010.
The problem I reckon happened when they brought in faster mobile parts. The newer dx10.1 40nm parts weren't capable of being fast and low power, so they went back to a previous gen for the faster "new" mobile parts. Which rather ruined their entire 3xx series line up. Because they both had to push the numbers all they way to 360(albeit GTS's, but the general public gets 360, and ignores the rest) and had to drop the mobile parts all to dx10 so the lower end parts didn't look better than the "new" high end parts.
AT that stage they'd used up to many numbers, points and different feature sets from what is basically a mix of the last 3 generations of parts all in one lineup.
I think at that point they just decided they'd better move up to 4xx series for branding because, frankly, they need the space in terms of branding.
I wouldn't be surprised to see everything from a 395-350gtx's, and a range of GTS models also, all off the 3billion transistor core, then you've got the cut down parts(if they make it this year). Fitting them all into the 3xx series lineup, as it is now, is just not possible.
If Nvidia simply ran into this situation blindly as per usual, or they wanted to have an excuse to try and make their new stuff sound even better than it was going to, who the heck knows.
