> "I had thought that TPB was blocked because of court orders.
  > So how come one ISP blocks it, and other doesn't?"

The court order[1] had 6 defined defendants:

  - BRITISH SKY BROADCASTING LIMITED
  - BRITISH TELECOMMUNICATIONS PLC
  - EVERYTHING EVERYWHERE LIMITED
  - TALKTALK TELECOM GROUP PLC
  - TELEFÓNICA UK LIMITED
  - VIRGIN MEDIA LIMITED

The court order only affected the listed ISPs (at that time, 94% share of the consumer ISP market). Other ISPs were under no obligation to do the same.

[1] http://www.bailii.org/cgi-bin/markup.cgi?doc=/ew/cases/EWHC/...