From what I understand, the production budget was $39. The rest of your dollar bills have gone on promotion, advertising etc. Of which, oddly, I have seem very little. Which may have been the problem to an extent.
Anyway, my four penneth is that it was a good movie... no, scratch that... a great movie. Best new sci-fi I've seen in the last ten years or so (sorry Mr. Lucas). It should have been a hit everywhere (not just UK) IMO. It wasn't. But it also wasn't a bomb by any stretch.
DVD sales do make a massive difference to sequel possibilities, if that's what's being discussed here. Even if they are direct the DVD sequels (which wouldn't be such a bad thing for Serenity - it's where Firefly was a hit, not on TV). Look at The Prophecy (fourth and fifth movies announced), The Crow (fourth movie, second direct to DVD out soon in the UK). Also look at The Punisher, a movie which pretty much followed the same cinematic path as Serenity (but without the good reviews), but has had massive DVD sales, and as such a (cinematic) sequel is being made.
It may not be the hit that fans of the show had hoped for, but I don't think the franchise may not be as dead as fan-site writers like Devin Faraci think. DepenRAB if Universal had a realistic expectation as to creating a ong term franchise, or if they just crossed their fingers and hoped for a lucky, one-off big hit. We shall see.