Actually, that makes perfect sence they want to find all pages on the Internet. Think of the Internet as a big web, well sometimes it is multiple webs and one web does not touch another web. This is a way for them to find non-touching webs. It is also a way to locate content from a niave or lazy webmaster. They are tilling the earth and they will leave no stone unturned.
I know for a fact that if you visit a page with GGbar that GGbot will visit it too!
There is a simple test. Make a webpage, place no links to it. Visit while viewing with GGbar, wait 3 months. And check if your page is in. I did this. And guess what! That page is now in Google.