I agree wih you and from his interview with the Speedway Star, Paul Bellamy was asked about London, but it is clear that Cardiff works for the British GP and he is not looking to go anywhere else.
Personally, I think Cardiff is a great venue with the Stadium in the heart of the town, where there is so much to see and do, plus pubs, cafes, etc.
The Fan Zone was a great success this year and will probably be repeated.