Basically the typical GTX 295 uses two sets of GTX275 with speeds set to that of a GTX 260 sp216 (GT200b), while the Asus GTX295 variant uses two GTX 285 cores, with GTX 285 speeds:
For GPUGrid crunchers the main differences are the 12.5% higher Core Clock Rates, 18% higher Shader clocks and features allowing for improved tweak-ability.
The extra RAM is irrelevant for crunching, as is quad sli.
Standard GTX 295; 576MHz Core, 1242MHz Shaders.
Asus GTX 295; 648MHz Core, 1476MHz Shaders.

Still the top card, for a few more weeks.

Asus may also have been flexing their muscles with NVidia. Either NVidia take one of their top customers to court over rebuilding NVidia technology, a lose-lose battle for sure, or they will have set precedence and be free to do it again. A difficult situation for NVidia saying as they sell chips to motherboard manufacturers too. Perhaps they negotiated so that manufacturing was limited, and they could maintain a respectable relationship.
It does not really matter how expensive they are, some mugs will buy them just because they are the top card. Both Manufacturer and buyer want to be labelled as makers or owners of the Fastest Card.