The rule is meant to be a deterrent. I doubt there is any terrorist who has a bottle of liquid explosives and reads the TSA sign and thinks, "damn, I guess I gotta throw this away".

While I'm on the topic, I read recently (can't remember where) that the proportion of successful detonations of a liquid explosive was actually pretty low, since many potential terrorists are killed in accidental explosions. As a side anecdote, we once had an FBI officer bring in a canister of some unknown liquid explosive for our group to test using our equipment, and I remember he was carrying it with the hand he "didn't use much" just in case it detonated.