That's a good point. Browsers are desktop environments with a built-in application runtime. Maybe it's the "Inner-platform effect."
It's an interesting idea to pull bits of the browser back into the system, or alternatively to write a desktop environment that's also a web browser (ChromeOS?).
A former coworker used Plan9 at a previous job, and he said it was cool how you could draw a rectangle on part of a terminal, and pipe that text (as it changes) to another process. Maybe rethinking GUI (and web in particular) from a unixy/plan9y perspective is a worthwhile exercise.
I grew up on Windows, and then there was the browser, and now everything is just the browser.