The Radeon HD 7990 graphics card is essentially two Radeon HD 7970s pressed onto a single PCB, with a built-in CrossFire link setup. The problem with this is that recently AMD has been having problems with frame latency, and though it has announced that it is working on new drivers to fix these problems, they aren't out yet. It appears that a number of people are holding off on buying this monster card.
For that reason, it wouldn't surprise us if indeed the graphics card will go out of retail in September. That said, other reports indicate that it won't be too long until AMD comes out with the next generation of graphics cards -- the Volcanic Islands series. The launch is said to take place in October, so a September end-of-life for the Radeon HD 7990 may not be surprising.