--maybe at one time but the BBC has advertising on some of its channels such as World--
Actually this is a common misunderstanding.
BBC World isn't really a BBC channel despite its branding, it's made for the British Foreign Office, like the BBC World Service on radio. That's why you can't see BBC World in Britain, because it's not meant for British audiences.
Those two services have always been separate from the BBC proper, and have never ever been allowed to receive licence fee funding.
The radio World Service is funded directly by the Foreign Office, and the advertising on the World tv channel is to cover the extra costs of television compared to radio.
--and receives a huge amount of money from programme sales. Some series sell to over 100 countries. In 2005-6 the BBC made over 600 million UKP from these channels which is around a quarter of revenue. --
A quarter is still only a quarter, the BBC could take or leave the money from foreign sales and still be able to make most of its programmes. The BBC isn't dependent on commercial activities and could give them up if it wanted.
Commercial broadcasters get 100% of their money from their programmes, either sales or advertising. They are entirely dependent on commercial activities, without them they'd die.
--Also I think even if you don't have a TV or radio, but use any BBC internet broadcast they can still fine you. (may be wrong on that one but my little brain thinks so.) --
I should think there are currently zero people who don't have a TV or radio but who have a PC at home capable of viewing video streams.
But that may change if they start putting BBC programmes online, it's a very interesting topic.