Such regulations do exist, as others have pointed out. And the issue isn't so much the shipping post office as someone checking the label along the way. Unlikely, but possible.

My understanding of the restriction on certain forms of batteries is that it's well thought out but, in cases such as these, ultimately pointless. Some batteries have a low internal resistance, which allows a large current draw, and potentially overheating. This is a real issue for for improperly packaged batteries since shorts are possible. I suspect that it is not an issue at all for batteries that are factory installed in consumer electronics. Unfortunately, the regulations probably don't distinguish between the two cases.