Editors are busy people. They would probably love to keep their slush piles down to, say, a two-week reply time. As painful as reading slush is, it's at worst comparable to YAMM (Yet Another Marketing Meeting). The realities of the modern publishing process, though, mean that most successful editors simply don't have enough time to subject themselves to slush—especially since most editors can't make the decision to acquire by themselves, but must convince at least two or three other people that the book is worth publishing and fits the publisher's plans. Since too many publishers don't really have a discernable, internally consistent plan, the latter can be a real bear.
In turn, this means that editors don't have the time for nonsense. Ms. Nielsen Hayden takes a lot more time for nonsense than do most editors (how many other editors at commercial publishers have their own websites that do anything other than discuss their cats?). Sometimes that nonsense gets a result that others might object to. <SARCASM> Of course, no author even engages in similar behavior. </SARCASM> Attacking the editor in question is not a way to either get ahead in the publishing world or even change behavior; so don't bother. Ms. Nielsen Hayden's correspondent would have been much better advised to work on his (I assume his) own material—whether that's writing fiction or whatever—than worry about one editor's opinion of an author whom she does not publish.
Those of us who lived through the 1980s remember Dress for Success all too well. (I almost always wore a dark-blue suit in those days. With four buttons and a whole lot of salad over the left breast, and lapel pins on both sides, and epaulets with shiny things on them, and… but I digress. Like that's a surprise.) Manuscript submission is the ultimate extrapolation of "dressing for success"—but, unlike the world of job interviews and salesmanship, there is almost no opportunity to overcome an unfavorable first impression. Sometimes that first impression can come from the signature block on the cover letter; and don't think that editors don't talk to each other about difficult-to-work-with authors. I know of one absolutely brilliant—not just my opinion, folks, but that of his/her professional society—scholar who writes wonderfully well, even in early drafts, but probably will never again get a contract from a major commercial publisher because he/she is impossible to work with, both in personality and in substance. That author's signature on a cover letter for an unsolicited manuscript (in the particular field in question, probably half the manuscripts published are unagented) is a near-kiss-of-death experience.
Publishers publish books. Editors work with authors and want to publish books. There is a difference; and failing to recognize and understand that difference makes an already-difficult buyer's market that much more difficult.