Now that I think about it, I read a lot of comics as a kid, and most of them were in all caps (or at least, they did not have two clear cases). It didn't feel odd at all that all speech in Asterix, Donald Duck or Calvin and Hobbes is in upper case. I bet most people don't even notice.

Isn't it weird that we spend so much effort to present text on computers in the way that we got used to specifically in printed books, once upon a time? The work that's been put into font rendering is crazy.

Early screens also were very low resolution and without thinking much about it there is more ambiguity between lower case letters than upper case.