I'm never sure. I've been literally dismissed by execs for a six-page reason written by multiple senior engineers why they shouldn't spend $20 million buying another company with "this is too long. Bring it back under a page and we'll read it."
I'm not going to try to parse Brin's response, but realistically, if Yegge had just written a page-length summary of his argument on this subject no one would have paid attention. Short-form writing lacks the scope to argue a point on factual arguments. It tends to rely on the author's personal credibility. In a large company, it's hard for people outside senior management to have the personal relationship with the CEO that's required to be persuasive with a short memo.
Engineering reports and academic papers get around the problem by including an abstract. It's not really the style to include them in informal business memos, but it might help in a situation like this.
It's foolish to ignore input in any form, but few people (even very bright, successful people) have the verbal bandwidth necessary to discuss important things solely via the written word. I tell people "business emails should be one short paragraph at most". (unless you are sure the other person can handle it).
I've noticed it in big and small companies alike. I think it's b/c when someone is checking email his/her mind is not in the proper state to pause and type a detailed reply to a 10 paragraph message.
It's purely a consequence of all the demands on peoples' attention and the ambiguity with which most people write/think. Face to face or even telephone interaction allows for ongoing verification of mutual understanding. For an example of how long and detailed emails sent/read by smart, capable people can create much confusion, ill-will and chaos, check out LKML :)
shrug
That wasn't at Google, though.