Dell's XPS 13 Ultrabook appears to have a user replaceable SSD, but not RAM. That Lenovo X230 appears to allow both. Seems other ultrabooks allow one or the other, or none.
While I do like to upgrade things myself (upgraded the RAM and put an SSD in my current 13" Pro) and would prefer notebooks have that option, Apple's targeting an audience that would rather have their notebooks be as thin as possible than have the ability to do something that they'll never care to do. People that don't like that, can just buy something else, in Apple's opinion.