We recently closed a maths usage question, Can I use both of setbuilder notations in one article?, which asked for whether it is acceptable to use two different comprehension notations in one article, on the grounds that it is off-topic. It is quite true that "a mathematical style question", as Ryan Reich put it, is not about TeX and Friends.
However, the question was clearly phrased in terms of TeX markup, and the semantics friendly approach to TeX can influence how one best answers these questions. Consider, hypothetically - what if there was a
comprehensions.sty package out there with distinct comprehensions
\funspacecomprehension, with a configuration command that allowed you to issue such commands as (excuse the ConTeXtism)
\setupcomprehension[point][separator=:], together with the configurations used in several textbooks?
In my opinion, the possibility either that such specialist support might exist for such usage questions, or might be desirable to have, is a reason for such usage questions to be considered on-topic, provided they have such an overt TeX&co. context. I consider that a usage question with such TeX-specific context is a different question, in that it asks for different kinds of answers, than one without.