I read Ender's game a couple times many years ago -- likely from the original 1985 book. After viewing the movie I recently reread the book from a later edition and was surprised to find one part match the movie which I was sure the movie had changed. Now I am wondering if I am remembering the book wrong or if the book was changed. I remember Rackham specifically ordering Ender not to fire on the planet (rather than giving him the choice) and that after Ender destroyed the planet there was silence in the command room (rather than an immediate explosion of laughter and rejoicing). I prefer the way I remember it (it seemed more emotionally powerful) and wonder why it was changed (if that is indeed the case).
Ender's Game was, in its earliest incarnation, a short story published in Analog in 1977. In that original, there's almost no backstory -- no Locke and Demosthenes, little about the politics on Earth, no mind game, no bullies, no post-war denouement. It's all about the Battle Room and then the simulator.
There is this exchange where Mazer (then Maezr) does forbid the use of the Little Doctor (not named as such) on the planet:
"Also, it's against the rules to use weapons against the planet itself. All right?"
"Why, don't the weapons work against planets?"
Maezr answered coldly, "There are rules of war, Ender, that apply even in training games."
However, the post-Battle celebration is still there:
He switched off the simulator, and finally heard the noise behind him.
There were no longer two rows of dignified military observers. Instead there was chaos. Some of them were slapping each other on the back, some of them were bowed, head in hands, others were openly weeping.
But maybe it's this version you remember?
Orson Scott Card has definitely revised the book, though I do not know what specific changes were made. While I have a copy at home, I don't have a second copy after the changes to compare it to.
In 1991, Card made several minor changes to reflect the political climates of the time, including the decline of the Soviet Union. In the afterword of Ender in Exile, Card stated that many of the details in chapter 15 of Ender's Game were modified for use in the subsequent novels and short stories. In order to more closely match the other material, Card has rewritten chapter 15, and plans to offer a revised edition of the book.>
I've read Ender in Exile, so I remember reading that afterword. It is based around Card's approximately one million billion sequels to one of the two good books he has ever written - the other is, funnily enough, the first sequel to Ender's Game, Speaker for the Dead - contradicting his original story; he therefore pulled a George Lucas, and altered the original, to its detriment.