I've always found windows system log too rich, actually. No too poor. Maybe largely redundant and therefore largely useless, but never inaccurate. Usually, you need to filter a lot before you find what you need.

And, while I believe there's no evidence of the shutdown as you say so, I've never heard of a windows box that does not log shut downs unless a system crash occurs. What I would not trust, actually, is XP telling you windows did not shud down properly at next reboot, as that is often unreliable.

Did I understand correctly that you do not see any record of the following reboot either?!?

Out of curiosity, "disabled" Windows Updates means it does not update automatically and you do so manually, or simply it does not update at all?