And, apparently depending on the style of your search terms or what you're searching for, one or two are better. I get noticeably better results from DDG, but I know that a lot of other people don't. I can only speculate that the difference must be search terms or topics.
For what it fails to find well I just prepend !g to my query and have it bounce me over to Google.
Google results are more often then not trash now, so I don't think the bar is too high for competitors now.
It does, yes, but not only Bing. At least report, it aggregates from about 400 different sources, and they also run their own crawler.
They used to have a list of the other engines they use, but I can't seem to find it anymore.