The question here is if the writers of emacs and NSIS care.

For NSIS, that's easy to answer. Considering it came from NullSoft, whose flagship product's slogan is "it really kicks the llama's ass", I think the answer is a resounding no. They wanted, primarally, to give the community making plugins for winamp to have an "installer that doesn't suck". They could care less if your management likes the style in which the documentation is written. In fact, style does sell, and the style with a decent bit of profanity is what sells to their target audiance.

Of course, as with many things emacs, their intent is largely "fuck if I know". However, promoting informality and usabilty is important to them, I think, and not frowning overly much at prophanity is part of that culture.