I agree with everything you’re saying there, about Progressive Enhancement, and device agnosticism (to a point - we can’t help it if people create really stupid browsers that are overly limited in capabilities, or insist on using browsers that are, then they may get the inferior experience and complain; but that’s not the developer’s fault, as at least it works).
However, I still feel like there are cases where considering support for IE1 or Netscape or the Internet Browser on my Kindle Paperwhite or whatever the crap we’re discussing are just… irrelevant. I’m sorry if that’s a point of contention, but… that’s just how it is. If people choose to make what are basically ridiculous decisions about what they use to browse the Internet, then I guess they’ll be frustrated.
You shouldn’t care about who’s using your site or what device they’re using. Everyone is welcome.
That is simply not true. There are countless web applications designed for particular groups which are not welcoming everyone. I’ll point you, to start with, to a company intranet.
Everyone is not welcome and it’s in a very software controlled environment, in some cases, to boot.
Now, do I think it should work on multiple browsers? For sure. I 100% agree with that. But is your actual argument valid here? No.
And you definitely should care. Having information and using it to make informed decisions isn’t bad; it’s good. And the general idea that we shouldn’t care who’s using a site is even more crazy! Have you ever heard of marketing at all?
TL;DR - I like the idea of PE in general. I love the idea of it for use on much of the web. But I don’t find a need for it across the board, and I find the idea that we shouldn’t care who uses our apps to be absurd.