People say that wrist locks/joint locks don't work either. However, I'm not going to throw something out because someone else says it can't/won't work. This could very well be because the people saying that, don't understand how to make it work.
The thing to keep in mind is that sometimes things will still work effectively, but you have to wait for just the right time to apply them. For example, take a joint lock. I wouldn't go in thinking, "Ok, I'm going to get his arm into a lock." but instead, "Ohhh...look, the arm is in a good position for me to apply this lock!" See the difference? Sometimes things need to be set up first. If during a grappling session, I want to get an armlock from the mount, if I were to go right for that arm, its going to be very obvious, where as if I tried something else first, as a distraction, I'm in essence, setting up that arm lock.
I hope this answered your questions.
Mike