WHen I google "git hosting", the first hit is git.kernel.org, then two stack overflow posts, then Gitorious, then GitHub. I wonder what my account contains that makes Google think Gitorious is more important to me.
I'd just like to add that a search for "git hosting" on DDG ("duckgoing" if you will) yields, aside from the SO quick info box (which mentions Gitorious and Redmine), unfuddle.com is the first result, github doesn't show up until the fourth of fifth, and I haven't scrolled down to look for Gitorious. It does, however, show http://git-scm.com/tools as the second result, which includes a summary of the most popular hosters divided by categories.
I'm unfamiliar with Google's indexing algorithm, but it's also possible that the rank of the top pages has shuffled between when Linus googled it and now.