answer:XTi is 2 generations behind, and it uses a digic II processor, as opposed to the Digic III in the rebel XS. The XS also comes on the market as an entry level unit, where the XTi was considered midrange. The new midrange camera is the T2i. The XTi came out in 2006, back when it’s components were still new, by the time the XS came out those components were generations behind and was discounted accordingly. I’m surprised the XTi is still being sold, it first came out in 2006. XTi also uses CF cards, XS uses SD.