...If they're close to 30GB, they couldn't do it due to space limitations, if it's much less, than it's probably a production issue.
HD DVD doesn't have a storage limitation issue!
Or more accurately: the biggest problem HD DVD has is bandwidth limitation, storage limitation is peanuts in comparison to that.
When encoding a movie, a decision is made how many soundtracks it will include, talking heads (PiP), subtitles, etc. That cuts into the the total bandwidth available on HD DVD disc (~36Mbps).
Because all this has to be loaded at once during playback (it sucks, but it's true, for both formats). That leaves a certain amount of bandwidth to the video stream itself (
and that is peak bandwidth!).
And then the encoding starts within those constraints. If you are left with 15Mbps for video (peak!) it will be ~7GB/h, i.e. 2h movie will take under 15GB. If it wouldn't be for audio, you can get away with a single layer HD DVD!
All this math was done before HD DVD was introduced as a format. The amount of thought put into it was an order of magnitude above what BD did (MPEG-2 & PCM). WMV HD (predecessor of VC-1) was tested and proven to be up to the task.
From time to time you hit the case where every last bit can be put to good use: 3h+ King Kong would be such an example.
VC-1 developers work on dynamic allocation of bandwidth (sharing between video and audio streams) but no updates were mentioned in the last few months. Network connection will be used extensively (if HD survives) to download any number of additional soundtracks/subtitles/PiP and store them in persistent memory (bandwidth limitation doesn't apply to it!).
Bottom line: with very very few exceptions VC-1 (dominating codec for HD DVD) has no problem to fit the movie into allocated space and being as transparent to master as it gets. It is when you want to accomodate those "Give me lossless or death! In 10 languages!" clinical patients you run into problems.
And now watch as the Blu herd chokes on the first sentence in this post and comes back with smart-ass comments like "Ohhh... A real nerve has been hit!".
Diogen.