I think the better question is, why the heck doesn't the US get any of this stuff. The blu-rays are shipped out of here for heaven's sake.
It just seems like Canada and the UK get much better stuff than we in the US do. Maybe that view is opposite in Canada and the UK, but man, why is it that the show was shot in the US, the Blu-Rays are coming from the US, and Starfleet Academy is even in San Francisco yet the UK gets Season 3 HD on TV in syndication before us. Hell, we haven't even seen Season 1 HD here and I don't think we will for quite some time.
It might be a rights issue. Doesn't SPIKE still own the rights to showing TNG reruns in the US?
CBS might be waiting for the rights to expire before letting the HD episodes air in the US. That way they can sell the episodes to a new network for more money.