Not that I have a dog in this race, but sometimes seemingly arbitrary convention can be exploited. For instance, some pioneering lad[y] might be compiling a collection of Ask-HN-questions. It's easy to see why it would be nice to have "Ask HN" in the title. Convention implies "easier to parse", and that makes programmers happy.
Not everyone uses the web interface. For instance, I read HN via RSS. If I see a post without "Ask HN" or a similar prefix, then I expect to be taken to an article. It's a useful nicety.