People say that but that does not mean that it is as effective as the squat.
When doing squats (and most leg exercises) you specifically want to target the muscles of the limbs (quads & hams) and minimise involment on the glutes and thigh muscles.
When doing pullovers, you want to work the torso and minimise stress on the limbs, (bis, tris, forearms). The shoulder joint is just so much more mobile than the hips that you can't rely on one exercise for it like you almost can with the legs.
Saying this is still believe that the cross-bench dumbell pullover is a key movement, along with:
Chins
Bent Rows
Deads
Squats
Low incline bench press
Dips
Military