I doubt there's any law in the US to prevent stations from using it for reasons other than traffic info, whereas I'll bet that there is in the UK.

On countless occasions I have noticed that local independent (i.e. non-BBC) radio stations transmit the TA beacon to switch you over to adverts preceding the news, which itself precedes the actual TA you are waiting for - most annoying.

That said, I would be inclined to agree with your suggestion that it's probably illegal to misuse the TA beacon here, no doubt the guilty broadcasters hide behind a legal loophole of some sort or another. Possibly similar to the one where advertisers use sound compression during adverts, a now distant rant of mine thanks to TiVo!