PhD student funding is guaranteed in my department, but not funding for M.S. students. Initially I did have a RA, supplied by my advisor's start up funding (he was fairly new at the time). But when his grant applications were rejected and his start up funding ran out, I had to do a TA instead. TA-ships aren't guaranteed though, and at my school if you stay too long on a TA they take you off of it to make sure that other students have a chance at funding too. My advisor did ultimately get some grant money in, but by that point there were other students who needed it more than me.

It might have something to do with recent state budget cuts (it's a state-funded university). My department has also grown dramatically over the past few years, both in terms of faculty and students, so the graduate student funding will probably lag behind for a few years more.