If you looks at these 2 pics you will notice that they are not the same.
has metal under fan, thus the heatsink. if you re-read the article
Originally Posted by btarunr
With the HD 7990, AMD on the other hand, borrowed the ventilation design of NVIDIA's GeForce GTX 590, to a large extant. It reused the fan found on reference-design HD 7850 and HD 7770, and placed it in middle of two heatsinks.
And now take a look at the 7990 pic
No metal because it is in the middle of both gpus. also notice how the top of the 7990 from fan to the right has slightly different PCB marking.