To be quite honest, it is not from a document, but from conversations with executives at both Star Alliance and other Star member airlines. I asked a number of pointed questions, and received some surprising answers...
There are minimum service levels and standards which must be adhered to...it is doubtful that these are public documents, but I have heard from more than one source that US does not measure favorably compared to other members.
My main point in the statement is that absent any agreement made between Parker and the Star Alliance with regard to US staying for 5 years in order to admit CO (which to me is now a moot point), I think US needs Star much more than vice versa...