If this is happening I don't care if it's a one ounce discrepency or a one pound discrepency. They shouldn't be doing this, and if they are, think of all of the extra money they're making with all of the packages of meat sold daily. Funny, I wonder why it's a few ounces under and not over? It sounds like it's done purposely.
OP, Next time you're at the store, take a random package of meat out of the pre-packaged meat case and take it to the butcher counter to have it weighed in front of you.