Sometimes, yes ("Desperation" was a bit of a slog, if you ask me). But most times? No. That I will deny. His first really successful novel, Carrrie, was only something like 70 000 words long. Another thing to remember is that, just because something is long, does not necessarily mean it's slow-paced. Misery had a bit of heft to it, and even though its main character was bedridden and could hardly move, it still had really good pacing, and created an amazing amount of suspense despite the simplicity of its setting.
If you want to talk about long winded authors, one of the worst offenders (in my humble opinion) is none other than JRR Tolkien. Holy crap that guy could go on and on about the most inane, inconsequential things.
Die hond pis al om die een bos, inderdaad... :/
(Says the guy whose novel is 1,2 million words long...) >.>
In SK's defense, they didn't stay true to the source material. But yeah, that whole thing was a monumental failure. I heard they did a pretty good job with IT, though.
Speaking of selling out, they're even going to turn Tommyknockers into a movie now, which even SK himself thinks is a bad idea. The whole thing is just one big gigantic metaphor for cocaine abuse. :/
You know, now that I think about it, I'm not entirely sure how much of a say SK has in which of his books they turn into movies, or even how they're portrayed. A lot of that might be up to the publisher.