I do actually agree with you about car tax. I did it online myself last time I had to renew it and it was very quick and simple. Which actually surprised me a lot considering it is the DVLA we are talking about here!
I'd say the DVLA's online tax system is one of the few government computer systems that works as you'd hope. It's great that it'll automatically check MOT and insurance and is really as simple and easy as buying from Amazon or similar.