Personally, I think 20mph roads are a good idea in the right areas. It's the ridiculous inconsistencies I don't get.

I have a house on the B4557 in a village near Aberystwyth. The B4577 is intersected by the B4337 in the middle of the village. At the intersection there's a pub, a bus stop, a post office and a kindergarten. Guess the speed limit.