At least with a public benchmark, people can point out flaws. With something rolled out internally, you're still likely to get flaws, but no one will point out that you misconfigured Postgres or set up Mongo the wrong way, or any of the other errors you are just as likely to make by doing it yourself.
Perhaps, once you've winnowed the choices down to just a few, it might make more sense, but I think good public benchmarks can be a helpful thing for that selection process.
