why wouldn't it sell? its faster then the 8800GT with AA and AF and its got a higher number (that not only translate to higher resale value, it also translates into more years of driver support!) If its cheaper to boot (albeit by only 30$) it is still a better purchase... nvidia could MSRP it in 100$, it will sell at its actual value just like the 8800GT and the 8800GTS 512 do. people aren't total morons, they buy it when the price is right... and merchants will sell below or above MSRP as needed.
I found all the latest cards COMPLETELY ignored MSRP and PERFECTLY positioned their price compared to what was available at the market at the time... if the 8800GT was X% slower then the 8800GTX then it went up in price to be Y% cheaper... and when the 3870 came out and was X% slower then the GT their prices adjusted to be Y% apart.. it might have not happened at ONCE everywhere... but if you looked for the cheapest deal for each card you saw them match those prices... (ofcourse, some places tried to rip you off by selling things at completely wrong prices... but I am compared the lowest available price online for each part)