According to various threads on here befpre and Digital Spy Warner and Sky have some sort of dispute and Warner movies are not going onto Sky in HD. You will notice others missing in times to come and there have been others since May that have gone AWOL.
Apparently, the speculation is that Warner want to sell the DVDs in HD but they (including Harry Potter) have supposedly appeared in Germany on TV in HD. So it seems a localised UK / or Sky issue.
If these claims are true (and if they are not then I apologise to our esteemed leader) maybe Sky and Warner just do not get on -perhaps merely a case of Harry Rotter and the Big Gob of Ire?
Anyhow I recorded it off Premiere - a whole 2% for two and a half hours.
This compares with a stunning similar length Narnia in HD off Anytime at 11% and an identical 2% HDD space for a mere 81 minute film (Stuart Little 2) off plain old Channel 5 !