Here's an article about this article: http://www.theregister.co.uk/2010/02/12/google_de_facto_internet_gateway/
Sadly, I know people who do this.. it takes much longer than either bookmarking or typing it straight to the address bar, so why do it? Sad, sad people.
People who aren't good with computers (and who are not interested enough in their more esoteric functions to learn more about them) often use Google (because a Google searchbar it is right at the top of Internet Explorer's window) to find what they want rather than type the URL into the URL bar or learn to bookmark it. They don't know what bookmarking is, and all those colons, acronyms, and slashes in the URL bar make it seem to complicated to bother with. It's not necessarily a matter of stupidity, it's a matter of convenience for someone who takes web-surfing as a very low priority. If you already know how, typing the URL or bookmarking the site IS faster than googling it. If you don't, then googling it is much faster than taking the time to learn the alternatives.
Since Facebook is just a way to keep in touch with friends and do other "real life" stuff, it attracts a lot of people who would otherwise hardly ever turn on their computers at all. It seems silly to us because almost everyone on this forum is an internet addict.