But fortunately that doesn't happen here. (Doesn't happen at the BBC news site either - no adverts.)

Agreed, it's no big deal sticking that indication in, most times anyway, and it's good manners. But it's no big deal either recognising a youtube link, whether it's specifically indicated or not, so looking to see whether it is is a good habit for dial uppers-to get into, since, inevitably, people aren't going to remember to put that indication in all the time.