Why is there an accent on ω in πώς when it is the only vowel present? Is it to distinguish between the question word and the non-question word (e.g. this is not how we do it)?
It is there to separate the question adverb πως=how, with the conjuction πως=that. Του είπα πως θα φύγω=I told him that I will leave, Του είπα πώς θα φύγω=I told him how I'll leave. In spoken Greek, there is also a difference in pronounciation, with πώς being accented and emphasized.
In interrogative pronouns with one syllable the only one I know that has no accent is ποιος/α/ο (sing.), ποιοι/ες/α (pl.) =who?/which? (whom?) in all declensions. Also τι=what? has no accent. Because there are not like them similar in written form.