We're still talking about it Tom, because you are incorrect.
The Message is the last episode as originally intended. Not Objects in Space.
Objects in Space is the REVISED last episode, the revised order was created when they put together the DVD set, but was not the original chronological order.
Forget the Airdate order, that is completely screwed up.
But there are two other orders to consider
Production order, and DVD order.
The production Order is the original intended Order, and is the actual chronological order. Had Firefly never been cancelled, this is the order we would all know and accept as fact.
But Firefly was cancelled.
In putting together the DVD release, Joss Whedon REVISED the correct order and changed up a few episodes, placing "Objects In Space" last in place of "The Message".
He did this because "The Message" was quite literally... "too funereal" So much finality to it for the series itself, not just the character that died. But this is only because it was the final episode made before cancellation. Had the show continued, it would not have been an issue.
Joss chose to switch it up and place "Objects In Space" last because the ending was more upbeat. It had a sense that their stories and adventures continue even though the show itself does not. Again, this was not what was originally intended, but what Joss chose to alter it to when putting together the boxed DVD set.
Actual Production Order (and correct Chronology)
1 Serenity pt 1&2
2 Train Job
6 Our Mrs Reynolds
8 Out of Gas
10 War Stories
Up til now, Both Production and DVD orders match... the remaining were altered for the DVD set...
11 Heart of Gold (DVD: Trash)
12 Objects in Space (DVD:The Message)
13 Trash (DVD: Heart of Gold)
14 The Message (DVD: Objects in Space)