Is this common?
I have a standard Dell computer so it's not like I have some oddball
hardware that's not supported as yet (presumably).
If you want to install SP1 for Vista it is freely available on
Microsoft's web site. Presumably the reason update doesn't offer it
for you is it thinks one or more drivers on your system aren't
compatible with the changes SP1 will make. At least that is the excuse
the fanboy crowd have thrown out several times.
Many people have reported issues AFTER installing Service Pack 1. So
unless you have a particular problem you hope SP1 will address I would
simply leave well enough alone.
I personally did install SP1 hoping it would finally resolve the long
annoying slow file handling issue. It did not. Now problems I didn't
have before show up, like stupid Com Surrogate errors.