Security bugs, what security bugs?
Here's the official change list from the Apple Update installer:
1. Performance improvements for Top Sites
2. Stability improvements for 3rd-party plug-ins
3. Stability improvements for websites with online forms
4. Accessibility improvements when filling out online forms while using 3rd-party screen readers
5. Improved memory usage when Safari uses a wide variety of fonts
6. Fixes an issue that prevented Safari from changing settings on some Linksys routers
7. Fixes an issue that prevented some iWork.com users from commenting on documents
See? It's all about stability and performance. And a couple of minor 'issues'.