When doing these "straight-leg deadlifts," I like too think of one of those bird toys that dips its beak in a glass of water, then comes up again. It bends only from the hips, and keeps the upper body in the same position throughout. That's what you should think of when doing the move: keep the upper body stable (shoulders back and down, chest up, natural curve in the lower back) then tip forward from the hips (not waist).
Aside from the hamstrings and glutes, deadlifts also work the lower back isometrically (you shouldn't be moving through the lower back, but there is tension there) and the traps (upper back) as well. Regular deadlifts (picking the bar up off the floor with bent legs) works these more than straight legs (but really not "straight" is in locked out : there should be a slight bend to the knee).