Yeah you would have to be a complete idiot to buy a 260 or 280GTX when you can get 2 8800GT's for $250. Nvidia really bombed this time.
I'm hatin on NVIDIA right now, but:
1. The user might not have a SLI board
2. The user might not have a good enough power supply
3. A single card generally scales better... it will be more consistent then 8800GT's would be.
4. The user may want to spend the extra on the newer GTX 260 now, so they can SLI it later. If you were to get SLI 8800GT's, your upgrade options would be limited.
5. The GTX 260 offers tri SLI
6. The GTX 260 has much better cooling.
That said, 8800GT's are still much better performance per $$$, and better then the GTX 260