It was always linear.
I think the issue right now isn't so much that it's linear, but that because the chains are so tightly bound together, you aren't given the ability to skip one or two quests. If you don't do them, you aren't allowed to progress.
Think about it like this in the fictional world of Outland with Cataclysm design:
You're going to Hellfire for the upteenth time. You know which quests you want to do and which ones aren't worth the time to you. So you skip them and by the time you're done with Thrallmar, you head over to Falcon Watch. But wait, because you didn't do every single quest in Thrallmar, there are no quests in Falcon Watch unlocked! Because you skipped something that you don't want to do, you're not allowed to progress at all.
That's how it feels. Thankfully, Outland isn't really like that. If it was, I'd probably shoot myself before entering it again.
I've never felt so constricted than I do with Cataclysm. I like the quests, but I like the feeling of saying "I didn't really like this hub so much, I'm gonna do the other ones first or skip it altogether"
Every quest is like an integral part of the story. Because of that, the game doesn't really like you skipping them. It's almost completely opposite of the way things used to be where pretty much every NPC had his own set of problems that needed fixing. Now every set of NPC is working together to make you fix the zone.