"I think the interesting thing to note here is that for most end users a standard protocol is not nearly as appealing as a standard user interface."

That is very true too. I often wondered what would have happened had someone created say 10 years ago an email client with strict protocol compatibility but employing an higher abstraction layer where discussions/attaches are managed automatically just like in a Whatsapp chat (chat -> mail list) using a similar UI. Probably most users would have rejected the idea because they had no intention to learn a new thing nobody was using. So, back to square one.