GTX means available, Ultra means unavailable...
 
We got a rather unexpected answer when we asked Nvidia why it actually decided to name its latest generation high end cards the Geforce 7800GTXs. The company decided to move from the suffix Ultra simply because its end users actually compared the suffix Ultra with the term unavailability.

Nvidia senior VP, Dan Vivoli, told the INQ that users simply associated themselves with the GTs as they always knew that they will be able to buy them. You could always get the Geforce 6800 GT card in the shop but not always the Geforce 6800 Ultra. It kind of makes sense that Nvidia sold more GT cards than Ultras as Ultra clocks are not that easy to reach and cost you some extra bucks.

It actually contradicts some older generations such as Geforce 4 where everyone wanted 4600 but barely anyone wanted its Geforce 4 4400, second in line cards.

Geforce 7800 GTX actually implies that there might be a faster version of the card called Ultra if Nvidia feels threatened by ATI's R520 card. Time will tell.


Source : TheInquirer