When Apple released OS X 10.6.8, a number of people found problems including issues with the printing system that resulted in print jobs hanging. To correct some of these issues, Apple rereleased the update as version 1.1 of the updater; however, if you have applied this update, you may (or may not) notice that your Safari version has reverted.
Apple released the original OS X 10.6.8 update before it released the latest Safari 5.1 update, and then released the revised 10.6.8 updater about 5 days after Safari 5.1 had been out. As a result, the Safari 5.1 update was not included in the 10.6.8 update and people who had been running OS X 10.6.8 and updated to the latest version of Safari will find their installed Safari versions will be back at version 5.0.5 instead of 5.1.
Ultimately this should not be much of a problem for users, as the versions are very close and should still support most of the same features; however, there is a possibility that the older version of Safari may handle a few things differently. OS X should detect the older version of Safari and offer you an update through Software Update, but if not, then you can download the latest version of Safari from Apple's software downloads page.
Thanks to MacFixIt reader Artie for the tip on this.