Well no, that doesn't make sense because the $659 GTX 780 SC has been available for many months now and already will easily compete with R9 290X in terms of performance. GTX 780 Ti will be a step up in performance for sure.
Makes fine sense, just like there is a 780 SC, there will be a 780ti SC. The specs make sense because they'll want to protect Titan's $1000 premium.
No doubt we will see a Titan-ti at some point with 2880cores and higher clocks for $1200+ or some such madness. But for now this will let them show a more reasonably priced card that can actually win a few benchmarks against 290X, which the 780 pretty much can't, and then move down the pricing of the 780 to compete against the vanilla 290. They don't think in terms of aftermarket cards, it's how their reference cards match up.
Sure is a silly card in my opinion, as the difference between 780, 780ti and Titan is going to be so hard to decipher it will probably come down to which card can overclock better than the other in the overclock lottery. But a necessary one because the 780 falls behind the 290X.