Planet13 - 5:48 pm on Apr 14, 2011 (gmt 0)
Because once they start quoting guidelines, they have to pretty much follow them - and even if they resist there's a good chance you can wear them down.
I am not 100% sure, but I think that is similar to following a "Yes Ladder" in persuasion tactics.
You ask them something small that you know that they will agree to (e.g., "You do think my content would be useful to your visitors, right?"), and then you steer the conversation so that they are agreeing to the value of more and more aspects of your proposal until they feel like they can't say no without contradicting themselves on points that they already agreed were valuable.