I agree with you completely. Since BBCA has an HD feed now, there is absolutely no incentive on their part to show anything further on HDNET. It would be a very bad decision to supply what is now "the competition" with prime material.
The promotion of BBCA HD, and the tie in with the Torchwood miniseries has been intense. If it hasn't produced results, I can only assume one of two things. 1) Most carriers are seriously bandwidth limited and adding another channel would be difficult. Or 2) the revenue stream from BBCA HD would not justify the expense and effort of adding it. Maybe both. They really need to do business in a business-like manner, as you suggest.
Actually if the priceis right it is in their interest to sell programming to the network that will pay the most for it and gereate more in advertising than what would be possible on BBCA. These BBC shows are funded by a "license fee" by all UK households with a TV. Their first priority for outside the UK is to sell to the highest bidder.
What you see on BBCA is not only content from the BBC but also from commercial broadcaster ITV (Primeval) and Channel 4.