The "umwelt" comic was even more complicated than that. It had different versions based on:

* location (getting surprisingly specific sometimes)

* browser

* what plugins work/don't work in your browser

* referrer (what you clicked on to arrive at the comic)

* operating system

* screen size

* browser window size

* hostname domain (i.e. you're at work, and your company's domain)

* hostname TLD (i.e. your computer's ISP is .net, .mil, etc)

Here are different compilations of the variations he created:

http://www.explainxkcd.com/wiki/index.php?title=1037:_Umwelt

http://imgur.com/a/faLz2

I'm not nitpicking, just helping demonstrate how far Randall went in that creation.