I think the version of Safari with 10.3 and later does block popups although I admit, I don't tend to use it, I'm more of a Mozilla person myself. As to Safari being "integrated into the whole OS", I don't think that's really true. KHTML is part of the OS and is used by various things such as the help viewer, but Safari is just another app which utilises KHTML. If you set another browser to be the default and delete the Safari application everything should run fine.
I understand that. I was refering more to the fact that it is the default browser and that other apps try to start it when they want to link to a website. But if MacOS is anything like windows or other OS then I imagine you can override this so that it starts FireFox or whatever. I'm just new to MacOS so I don't know much about setting these things up.
It also comes on the install CD/DVD since 10.3 as an optional install.
I was meaning to have a good look at the "install" discs. Regards