I agree with this - Everyone is of course absolutely free to customize and tweak their installation, but this is not what it's about. It's not a "brand" issue (but it's a nice side-effect, of course).
We don't know anything about the person asking for support - Neither their technical knowledge respectively skills nor their current setup. We should assume they're on stock and their skills are minimal. Even when this does not apply to the questioner, it might apply to people looking at the answer later on. There are quite a few people out there who do face problems when things aren't looking the way they're supposed to do (I guess everyone knows the stories about people saying "I deleted the internet!").
elementary OS is supposed to be an operating system even for the more-or-less computer illiterate - By providing "standardized" instructions, we make problem solving for all kind of users easy. Some are already "challenged" by the information / fix itself, let's not make it harder for them (by providing various looks and settings in screenshot instructions).