It's more about extending the life of your video card purchase...say you grab a 6600GT for $200...1 year from now you could get another to do the SLI for prolly next to $100 and get quite the performance boost...sure beats forking out another $200 on a replacement that might perform around the same as having the SLI...
But dude, THATS ASSUMING you already have a dual pcie capable mobo + hotup ram + hotup cpu aka already have cash to burn.
My point is, for someone who can afford such in the FIRST PLACE...saving measly ~100us say 1 year from now is rather insignificant.
To that person he'd have to do complete upgrade to mantain the same kind of \"edge\".
Remember who this is target for...and take note who actually will shell out for this kind power...
In other words Nvidia marketing to the lowerend is faulty...at least until everything become drastically cheaper all round.