It's been an odd running theme for me today that I've misinterpreted posts. Up until your final sentence, I thought that the thesis of your post was:
The standard document may say one thing, but what people do in the real world is the real standard. If your software has issues with the world's most popular IMAP server, you need to adjust your software to be compliant with the standard.
I'm personally more sympathetic to your actual conclusion, but it's odd how often a single argument can be used to support two conflicting beliefs.
Yeah, agreed! I titled my guide "Practical IMAP" for reason (and almost called it "IMAP As She Is Spoke"). The standards are useful to a point, but actually to jeffbee's point the internet has evolved a lot since then, and how to actually work with modern email is a pretty underdocumented - including by Google themselves on the Gmail-specific parts.