Those are two entirely different things - or even three entirely different things if you're going to consider Rome "funded by the BBC" when it provided fifteen percent of the budget.

Spooks for instance is, as far as I'm aware, simply a British show - British actors, British makers, British money. Game of Thrones may be largely filmed in Britain and have many British actors, but it's made by an American company and American producers. Rome was mostly American-funded and made, with some British actors. I can't see how Britain would deserve the majority of the credit for either of these last two.

It's a bit silly to consider shows Canadian just because they're filmed (generally not even set, in-story) in the Vancouver area - or because their lead actor is Canadian.

I guess I'm not following American television so closely that I can judge how it is now compared to just "a few" years ago, if by "a few" you mean only two or three. But American companies - and not just HBO - have produced numerous excellent shows in the past years. Just because an increasing amount of these shows has foreign participation in either the funding, the acting or other roles, doesn't mean they're not American anymore. One of the many reasons why Lost was so good was its having a significant international aspect in actors, characters, setting and story, while still being backed by the huge American knowhow and funding possibilities that few other places can match.

I don't think American television is growing worse. Non-American television is growing better and the gap is growing smaller, is all.