I think what we have here isn't a deliberate effort to extinguish a standard, but a clash between two different cultures. LKML follows traditional hacker norms, from the days of actual terminals and slow connections, whereas Outlook is built for the world of GUIs, WYSIWYG, and more or less high-speed connections. The latter is what the vast majority of people have chosen, so it's a sensible business decision for Microsoft to not pay much attention to the old ways. It's just unfortunate when those two worlds collide.

I appreciate your sentiment, but I don't know, I'm not convinced. You can have all the GUIs and WYSIWYGs you want, but as I said, email replies should default to the same format as that of those received. Thunderbird (a modern email client) does this, if I recall correctly. It's very easy to avoid this mess.