Less about 'of their size' then about how long they've been around, since back in the days when a large company could get a /8, and just about anyone could get a /16.

Interesting. I know Google uses the IP 8.8.8.8 (and 8.8.4.4) for their public DNS servers. So it seems Level3 doesn't own the entire 8.0.0.0/8 block then.

They do, but they reassign some of them to other parties: http://whois.arin.net/rest/net/NET-8-0-0-0-1/children

Yeah, that was what I meant, brain error. Thanks, I edited my comment.