This is ancient, it's been like this since before I joined Google, which was before Bing came out. I think back then Dogpile was #1 (??), then Yahoo, then MSN Live. Occasionally it comes up and people get a good chuckle out of it.
So honestly, shouldn't google show up as the top result for search? Does the fact that it doesn't prove that Google does, occasionally manually 'fudge' search results?
Well, why would google put itself as the top search result, when you are already on google search. And also, recently, there was some complaint (don't remember exactly who filed the complaint) about the anti-competitive movement of google when it comes to always showing google maps results when searching for locations. Anyhow, just my view of this.
Maybe not. Google is so generic that there might not be as many links to Google -- y'know, 'cuz why do you need to link to Google -- as to several of these other engines. It's not totally impossible that some other engines would have a higher ranking organically.