Logging in for the first time in years to reply to this.
Why not paying from the taxes? Because the programs can then be politically influenced! That's why.
You'll hear complaints in the Murdoch owned media that the BBC is left wing and biased. Trust me, after the Netherlands did away with the license fee (because it was cumbersome and people didn't understand why they had to pay for it) and switched to a tax payer funding, the usual suspects (usually on the right side of the political spectrum) have since started influencing and outright adjusting the content.
In the Netherlands the long treasured pluriform system is now on the verge of collapsing under the weight of the ratings. I wouldn't go as far as saying the content is politically influenced, but the system is not completely without government influence either. The way the BBC is funded is actually very clever, its fee is set outside the political cycle. Here is some more info about this scheme: http://www.bbc.co.uk/blogs/aboutthebbc/entries/9637e45d-c96c-36c6-9e3f-af141e81cab4 (Sorry, don't know how to make a hotlink on Slashdot)
Quite a few people inside and outside the UK truly understand the value of the BBC. It goes far beyond Top Gear, don't believe the Murdoch owned media lambasting the BBC.