It seems like the Software Update engine and the underlying installer are unable to restart newly installed services on their own. Also, this update fixes (updates) OpenSSL, on which other packages depend.
However, I think Apple _should_ be able to fix this in a later version of Mac OS X. It's only sad that it keeps my uptime low, as I think I would now be up on my PowerBook since 10.1.3, if I hadn't updated anything. But then again, we _want_ to update, don't we.
And isn't rebooting in Jaguar fun? You wouldn't ever see that the smiley Macintosh icon is gone from the boot process, wasn't it for the Security and Feature updates we're going to get soon.