Thank you. It looks like Postdesk started a public controversy while leaving out two critical pieces of information:
1) William's actual e-mail, which expresses his disappointment in a reasonably polite fashion. Normally, this sort of e-mail should merit a polite response and a refund.
2) The allegation that William send the email to the entire engineering team (http://news.ycombinator.com/item?id=2152203). This changes the context of Karp's remarks significantly, because it means that Karp had to weigh two things: The feelings of a disappointed customer, and the morale of his already-stressed engineers.
In this case, I actually sympathize a bit with Karp. He needs to take care of his customers, but he also needs to take care of his people. That puts his remark "...we have no interest in customers that will go out of their way to discourage our entire team..." in a rather different light. That's not an easy situation to resolve well.
I wish that Postdesk had provided more facts (and less editorial comment) in the original article.