I am curious, what are the legal implications of publicly publishing their query (aside from publicly carping about it)?
Is there no sort of client-vendor confidentiality agreement (spoken or unspoken)?
Well, in strictly general terms, [but not necessarily legal] you can pretty much do whatever the hell you want on the internet (aside from child porn) as long as your ISP backs you up or your ISP is based in a country that makes it very hard to legally pursue, like China or Russia. Child porn is the only thing Interpol really clamps down on internationally. If I posted your query letter here, since I'm anonymous, your main legal recourse would be to ask blogger to take it down, and blogger would probably not care enough to make me do it. If I wasn't anonymous, you could report me to the AAR or the BBB, or various other guilds, but it wouldn't come to anything.
That said, I'm not going to post any query letters. I mean, aside from that spamming anonymous jackass. Yes, it is an unspoken non-client/agent agreement, because we're nice, and don't generally like to piss off writers. Actually, most of us like writers, as they are the thing that makes our business exist and we base our careers on making the good ones into stars because we love literature. It's why we're in the exciting, low-paying world of publishing.
My general policy is not to post people's email addresses or even letters in entirety unless it's a question they obviously mean for the blog and I want to answer it on the blog. That's just common courtesy.