Sure they don't. Why don't you go down to your local pool hall with an ACCURATE scale and measure the cueball, comparing it to the others. (Obviously that only applies to matched sets of high quality balls). Close to spec. is nothing to be proud of. Pool ball specs, along with all other significant pool specs are ridiculously tolerant. This is because the equipment manufacturers have had too much power in pool. The range of weights can vary by as much as half an ounce! That is INSANE. It's 14 flipping grams and no tolerance requirement is given, so guess what that means? A top of the line snooker set is within 1 gram, the tolerance permitted by the rules is 3 grams! However no standard weight is given in snooker, so in that regard they are more permissive in theory.
In my experience the best Aramith sets are within 1 gram. Mine were, I haven't measured them in a while, but maybe I will (super pros). My pool hall ALSO has Super Pros, and let me tell you, those balls are not EVEN close to being as factory new. The weight varies wildly.