Why would they change the ending?![spoilers obviously]

Because this is basically the tradition of all the Clive Barker adaptions. They all have major changes to the original story to give different expieriences. This was done to Hellraiser, this was done to Nightbreed, this was done to Lord of Illusions, this was done to Book of Blood, this was done to The Midnight Meat Train and it was done to Dread.

The original story is about irony, this is a twist to the adaption. Does it make a better story overall? Not really. But i think this film made Quaid a more interesting character

I refuse to argue on IMDB until the general populous actually uses their brains

"Hollywood" didn't make this movie.

In the short story, Stephen and the deaf guy are the same character (they split him in two in the film to fit the movie format). Basically, when Quaid captures Stephen he locks him in a sensory deprivation room that makes him remember when he was deaf for a short time during his childhood, driving him insane kind of like the deaf guy in the movie. Quaid's motivations in both versions are the same.

The differences between the story and film, however, are pretty substantial:
-In the story, Quaid really does seem to let Cheryl go, although she's completely insane afterwards. This is all told through his perspective, of course, and is thus not totally reliable, BUT it can be inferred from what happens later in the story.
-In the story, Quaid had a phobia of clowns (which the movie directly mocks through Quaid's dialogue by being pretentious and saying that fear should be deeper). He tends to have nightmares about them.
-In the story, Quaid does nothing to prevent Stephen from escaping (thus implying he really did let Cheryl free). Stephen is completely insane after his torture just like Cheryl in the story (and the deaf guy in the movie). In the story, Stephen wanders around town and stumbles into a homeless shelter (I think it was a shelter...it's been a while), where he is mistaken for a drunk bum and given baggy clothes. By this point he is extremely pale and his lips are red and chapped. They put the clothes on him and leave him be. This is when Stephen grabs the fireaxe in the story.
-Quaid's sleeping in his apartment until Stephen breaks in (kind of like in the movie). However, the events of the night make Stephen unrecognizable: his face is deathly pale, lips red and bloody, and he's wearing baggy clothes--basically, he looks like a clown. Quaid pretty much craps himself in fear and the last line in the story is something to the effect of "the worst thing in the world are dreams come true," implying that Stephen kills Quaid. It's still not a happy ending, since NO ONE in the story walks away sane by the end, but at least the villain gets his just desserts.

They changed the ending so there could be a Dread II if the first one did okay.