Why? Do you know how much it cost to have HD channel? Do you know how much Band width it take up? For what, a 30min promgramme, and nothing really else. Its not cost effective.
With DQF and the BBC's coffers being severely restrained, it's not worth at the moment converting regions to HD at the minute.
There's no way that the BBC will convert multiple regions for such an expensive sum!
And with how HD channels cost to run - you only have to look at the large amount of services locked behind the Sky and Virgin paywall.