Microsoft recently announced a schedule for Windows Vista Service Pack 1. They'll be launching a beta in a few weeks, and the final pack will be out at the beginning of next year. This is surprising because up until this point, Microsoft said they had no plans to release a service pack for Vista. What's really going on is that Vista sales have not been going well, and Microsoft is throwing a bone in hopes it will spur adoption.
Traditionally, most companies do not deploy a new Microsoft OS when it's first launched. They're often unstable, and it's not wise to trust your business to something so new. It's usually not until the release of the first service pack, which usually fixes a large number of issues, that companies will finally roll out the new system. After 15 years of this cycle, it's now ingrained into pretty much all System Administrators and IT departments. You simply don't roll out a new OS until at least Service Pack 1.
Meanwhile, Microsoft has been hard at work on the "update" issue. Typically OS updates are a pain to deal with, and these days they come out at least once a month. Because of the volume of updates, manually updating is just not feasible. To deal with this issue, Microsoft came up with Windows Update, which automatically downloads and installs updates. This reduces the load on Administrators (theoretically), and allows Microsoft to update more frequently.
With the roll-out of Vista, I believe Microsoft planned on avoiding the Service Pack thing altogether, and wanted to use only Windows Update.
Here's where the bone comes in...
Because of the traditional waiting until Service Pack 1, most companies have not implemented Windows Vista. Forum and blog posts all over the place commonly advise "wait for service pack 1". Microsoft has tried to overcome this perception, but their own actions reinforced the habit for too long. From what I've seen, Vista has been incrementally improving every month, but incremental updates don't have the same perceptual punch as whole service pack does.
What I think is really going on here is that Microsoft decided to whip up a service pack, release it, and hope that those who are still on the fence will finally pull the trigger. This service pack is really meant as a patch to their market perception, as opposed to something really new for Vista.