Fair point; spoken like a true broadcaster - however us Virgin subs do pay a premium to access what HD channels there are. Ditto Sky subs.
At present BBCHD is not a simulcast (I know there are plans to to launch BBC1HD which will be,and will therefore create issues of its own) and provides a mostly full HD output, but the rest are simulcasts providing a mix of source material and your point is therefore well made. Given the caveat above.
Film4 is a different issue. Film is an HD medium. 99% of what Film4HD shows is 35mm and there is no excuse not to show actual HD masters or at least remaster (even if they don't do a full clean-up/restoration) the print into HD. Although, most distributors now offer the majority of their library in HD, so why not? So BBC - watch out. You're planning an HD movie channel. Make it right.
But there's another issue. Anyone with a 1080p screen (and/or a reasonable AV amp) already upscales everything automatically. There's no real benefit in having the broadcasters do it for them. Are you really telling me that you broadcasters do it so much better? Is it worth the premium? Is it worth the extra space it takes up on my hard drive when I record it?
I take the point that a simulcast creates problems and having it for the 25% that's in true HD makes it worthwhile. Arguable, but let's accept it for now. But what should - and must - happen is that EPG notes (you know - what's behind the 'i' button), say clearly whether it's upscaled or native just as it notes repeat, widescreen or stereo.
Then we can make some choices correctly informed.