Sorry, but I can't agree with you when you say "many folks are not writing code for ancient browsers anymore".
A LOT of people are still coding for ancient browsers! More than 20% of people at China are still using IE6!!!
I am still supporting IE6 not because I like it (I don't!!!) but because the target of my clients are using it.
I would say, yeah, it's true, hmmm, actually if were going to think of it, it is just going to be a waste of time, but since compatibility is important to make a good user experience, most of the developers are still coding for ancient browsers, since there are still some that are not that updated with their browsers..