They should be, to put the users in the Q&A mindset; instead of in the discussion mindset, which happens when the question titles are not in the question format.
What is meta?
- Any Stack Exchange user can ask a question
- The community provides support, votes on ideas, and reports bugs
- Your voice helps shape the way Stack Exchange operates
Where they're not, people can (and do) edit them. It'd be a bit difficult to enforce this programmatically. Imagine if you got this error:
Some users would just do this: "format this date?", which isn't any better.
The only solution to this is for users with sufficient reputation to edit questions which aren't titled as questions.
Does it really matter? As long as people understand what you want, that's the most important aspect. The question can be in the body, I don't see a problem with that. Most discussions usually take place in the comments (if at all).