The TV Licence is payable for all households who have a TV and computers capable of receiving and streaming live broadcasts over the internet.
It is a tax, but without it, do you really think that Top Gear would be so awesome?
Seriously, they'd have to bow down to advertisers and sponsors to a certain extent and that could bring their objectivity into question.
Plus, if you don't have to worry about sponsors, you can take risks with high concept programmes. Things like Life on Mars, Red Dwarf, The Sex Olympics.
That's not to say that the BBC doesn't warrant any criticism. For some reason, they only seem to allow idiots for DJs on the daytime slots on Radio 1.