If questions pass the test described here, namely that A) they're motivated by a desire to understand and/or practice Judaism, and B) it's reasonable to expect specifically those who base their lives on Judaism to be especially capable of answering them, they're on-topic. Otherwise, no. Some "How many X in Y" questions meet these criteria, but not all.
So, here's the thing. I have, in my nearly four years on the site, been assuming "questions about a Jewish text are on-topic" means to say that any questions about a Jewish text are on-topic. I have been voting to keep these questions open as not being off-topic (though in some cases I've voted to close for reasons irrelevant to this discussion). But in digging through the FAQs on the topic, that's not so clear-cut to me anymore.
First and foremost, the main in-scope FAQ:
If you have a question about...
- a Jewish text (explaining a passage)
...then you've come to the right place. Please, ask away!
The sample questions definitely take "explaining a passage" very literally, in that only questions asking to explain a Jewish text are listed as examples of on-topic questions under this clause.
Similarly, in regards to fact-checking Judaism:
The pursuit of information needed to understand a Gemara properly is certainly in that realm [of being on-topic]. [...] Knowing if the facts found in the simple reading of the text are accurate is essential to understanding what to take away from the text and how to interpret it.
Is it necessary to know how many words are on a page of Gemara to understand it? No, not at all.
Maybe we can defend it based on our criteria for Jewish life questions?
I believe that the guiding principles (though not bright-line rules) for on-topicness should be:
Is this question expressly or implicitly motivated by a desire to understand or practice Judaism?
Is it reasonable to expect that a group of people who base their lives on Judaism would be especially able to give informed answers, due to their basing their lives on Judaism?
Are such questions "motivated by a desire to understand...Judaism"? I don't think so. Would "a group of people who base their lives on Judaism be especially able to give informed answers due to their basing their lives on Judaism"? Definitely not. Anyone who knows how to write a script to automate the process can count the words easily enough. You don't need to base your life on Judaism to be especially able to give an informed answer to these types of questions.
Not all X in Y questions are created equally
Consider the following variations on your "How many X are in Y":
- "I'm just wondering." As per the above line of thought, these should be considered off-topic, unless the OP edits them to match one of the on-topic examples below. (Some questions currently open which fit this rubric: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. These can almost all be easily edited to fit in with one of the on-topic categories below.)
- "I'm trying to make a study schedule" or some variant thereof (examples: 1, 2, 3, 4). These types of questions aren't just asking for statistics of Jewish books because they're curious, not because it has anything to do with Judaism. They absolutely pass the "motivation to practice Judaism" test, since they're asking for these statistics within the framework of how to divide up their Limud Torah.
- "I'm aware there are different minhagim" (examples: 1). These questions ask about X in Y statistics which might vary based on different minhagim, and are thus "motivated to understand Judaism."
- "I want to get a sense of how big it is and to compare with other texts" (examples: 1). This fails all the tests above and therefore is IMO off-topic.
- Calendrical questions (examples: 1). These ask about how our calendar are structured on a fundamental level, boiling down to the rules governing how days are distributed, and are therefore "motivated to understand Judaism."