Ghostcrawler has a nice long screed over on the forums about Blizzard's theory about change. Way back when the first few patches went into the game, Blizzard had a plan to adjust a few classes at a time -- one patch would be all about Mages, while the next would be about Rogues. But right around Burning Crusade, they changed their mind -- no more large patches, and instead it would be back to lots of smaller changes.
Of course, nowadays, whether they mean to or not, we're back to the way it was -- patch 3.1 will have pretty huge changes for all of the classes, and everyone is getting a free respec. GC says that while the "progressive patching" idea was a good one, Blizzard just doesn't have the chance to take that time -- patching is a big undertaking, and the way they change the game just plain leads to putting a lot of changes in a big patch. He would love to have the team make smaller patches more frequently (tweaking instead of a complete revamp), but the way things are now, the system just isn't set up that way.
He also reiterates that Blizzard is designing the game, not the people who complain on the forums. Blizzard listens to what their customers have to say, but they make their own decisions from there. Sometimes, that means we complain about problems that don't get fixed (Cower bug, anyone?), and sometimes it means they hear us complain about things that turn out not to be a problem (back in beta, a few forum posters claimed Death Knights would never be able to tank, and we now know that's clearly not true). We can hope for more sequential changes in the future, but GC says that right now, the way the game works is that Blizzard fixes as they can, and those fixes will come out in large chunks like 3.1.