Why are Updates available via microsoft downloads but not w/ Updat

This might just be an issue with timing, but I thought I would throw the
question out there. In short, why is there an update that is available via
www.microsoft.com/downloads that is not found when using the embedded update
tool in Vista?

Some background:

There is an available update for the iPod "safely remove" bug (Update for
Windows Vista (KB933824))

I found out about it when I was downloading the latest version of iTunes and
it pointed me directly to the patch.

Rather than simply download it from the linked page, I thought it might be
better to see if Vista had already updated itself with this patch, so I
checked my installed updates and it was not listed.

I then ran the update program to manually check for updates...it found none.
I have every option set to automatic and the updater set to look for all
updates, not just windows.

Is there a delay between the time a patch or update is released and
available via microsoft.com/downloads and the time that the Update tool has
access to the same patch or update?

While not optimal, I can certainly understand why Microsoft wouldn't want
millions of machines hitting its servers all at once for an update. Mainly,
I'm looking for some assurance that this is normal behavior rather than an
indication that my system is have issues.

Thanks for the help...