i later saw a similar report in the bbc.co.uk buried under the tech section, hence the edit.
the reason i was surprised about the ads is quite simple. bbc is paid for by uk tv viewers. basically if you own a tv you have to pay a license fee. in return, the bbc does not do ads (on tv/radio at least) unless you include the ads about their own programs. and i think they don't run ads on their main site (the uk one).
i'm guessing they are running ads on the international/american/whatever version of the site (bbc.com) to pay for the running cost so the british taxpayers are not in effect subsidising that site. i wonder what kind of ads they run.