Indeed; the alternating nature of AC means that it doesn't cause a prolonged contraction in the muscles, so unlike DC it doesn't usually cause the victim to grip the voltage supply.
As for the "no shock is safe" thing, depending on the location and the current of the electricity, some shocks can be perfectly safe. For example, nerve conduction studies involve stimulating a nerve with a small electric shock and measuring the time taken for a reaction at another location along the nerve. These studies take place regularly and as far as I'm aware there have never been any adverse health effects recorded as a result.
On the other hand, an electric shock which travels through the heart or brain may cause a myriad of health problems, even if there initially appears to be no problem. It's partly this reason that, for example, conducting a current to ground from a hand through to a foot, is generally much less likely to cause serious injury than from hand to hand, where the current is very likely to pass through the chest.