Absolutely. Those you suggest there are good examples.

Good enough that, instead of "is/isn't" programming language, it would be more a "ah, so, how do you define that then?". Now that I've had some sleep, one could argue that I could have been nicer and suggested that approach for HTML as well. After all, it's just words that mean stuff, and transfer a concept between people, that translate to the same (ish) idea. The moment the latter isn't the case, it's no longer very useful for the former.

Most disagreements, I find, are just cases of different understandings. Discussions worth having is when both are correct but different, and both want to figure out why they differ. So, on second thought, I think I was appropriately rude ^_^

Both LaTeX and roff are Turing complete, but they are also DSLs with a somewhat narrow "domain". Sounds exactly right that these blur the lines between what is/isn't. You could even argue that claiming one or the other is just one way to express how you understand that difference.