Also, we've reported in the wrapup thread that the pre-owned version is $24.99, and you can get an additional 30% taken off on top of that. $17.50 isn't a bad price for Splinter Cell at all.
I noticed that too. You have to go to the pre-owned x-box section. If you select the "T" titles, it shows up as $24.99. If you just try to access splinter cell from the front page, it shows $44.99.
It's probably to continue selling on the Xbox. It recently got released on the PC, right? In Ghost Recon's case, they took a year old game and released it on the Xbox. By that time, the PC version of Ghost Recon already had a decent price drop.