William Holman Hunt, 1852,
Tate Gallery, London.
All it needs is for a person of influence (read agent or editor) to articulate a personal taste about the submission process and within days it becomes a canon cannon, fired off hither and yon all over the place.
Agent Nathan Bransford, for example, does not care for queries that begin with questions - questions usually described as "rhetorical".
If I were an agent, I wouldn't either - I'd prefer a query to get to the point immediately without oratorical flourishes.
But I have noted that other agents, on occasion, have indicated that the question form of introduction is quite acceptable in their eyes. And Nathan has emphasized, more than once, that this is his taste and not a universal standard.
Further in these instances, a short 'n dirty definition soon makes the rounds - one that asserts a rhetorical question is one that doesn't have an answer.
Oh, sheepshit, Batman.
A rhetorical question is a pursuasive device that does not require an immediate answer from the listener. It is not intended to evoke an reply, rather to create anticipation, interest, a suspense. It has also been defined as a question that won't take Yes for an answer.
A rhetorical question is like the lights going down in a theatre, like a trumpet to open an assembly, like an "all rise" in a courtroom. Its purpose is to give notice - to emphasis the importance of what is about to come down.
It is a technique that demands you shut up and sit down and give the poser time to lay out his answer. Which is why, in query terms, the device might be considered a rather unnecessary, mind-game, preliminary.
The real question is not type, but taste.
And sometimes, a question is just a question.