dcharlie, they are fairly niche. I think most of them are probably too risque for network TV, so they are stuck on either PBS (whose programming is different area to area) or on cable networks. So naturally, they don't get a whole lot of exposure.
Non-comedy BBC/British shows are like, basically nonexistent in the US. I'm not even sure how I originally got exposed to Touching Evil and Cracker. Actually, it was probably my brother, since he spent a bit of time in the UK.