I agree, but I think writing that in a long email where you bold that sentence is pretty condescending. I think that's the main issue people are taking with it. If you want to engage in a discussion about cultures and platforms, I think that's a valid discussion, but this email was not the place to do it.
Actually considering he was asked WHY he didn't choose them it was the perfect place for it. The fact that he bolded that line only served to highlight his real and only true objection --- the development environment. Everything else he addressed was secondary and he would have probably taken the job even with all those other points. After the interview it really doesn't matter much what the interviewing process was like, but the development environment is something that will be with him everyday.
His whole email could have been summed up as "you're on Windows, I don't do Windows". That's not condescending, that's his preference and HIS reason for not taking the job.
The fact that he bolded that line only served to highlight his real and only true objection
Maybe. "Rather, the same initial rejection would occur, for the same reasons; and the search for justification, afterward, would terminate at a different stopping point. [..] This might be an important thing for young businesses and new-minted consultants to keep in mind - that what your failed prospects tell you is the reason for rejection, may not make the real difference;" -
http://lesswrong.com/lw/wj/is_that_your_true_rejection/
"It may seem arbitrary, but the platform an organization uses is indicative to me of a whole lot."
What is he supposed to add here to avoid condescension? He was asked a question, this belief drives the answer. He admits his opinions might not be fully formed ("seem arbitrary"), and claims no general truth for his opinion ("indicative to me", rather than just indicative). And he's giving his basis for preferring Unix, rather than a vague "I don't like Windows". He's actually not negative about Windows at all!
