I think there are several elements at work here:
Obviously the OP is looking for a solution and either can't be bothered to look it up or learn. As you point out, sometimes they appear to demand an answer, but some of the time this is down to english not being their first language.
The fastest gun in the west usually gets easy rep for basic regex answers - I've seen cases of the same regex being provided and each answer get the same upvotes.
Some users effectively wait on tags to build rep and I've seen the subject discussed on meta: 6 simple tips to get Stack Overflow reputation fast (old, but valid)
Regex is (or can be very localised at times) - some requiring very specific answers, yet of some complexity (or even an alien language) to beginners
The better answers usually include some form of reference to attempt to help the OP learn (although they are few and far between most of the time)
The more sophisticated regex questions aren't answered anywhere near as quickly...
In terms of down-voting answers to bad questions, I'n not convinced that's a constructive idea, but when you have a new user who is a bit wet behind the ears, I'd rather see accurate/good answers to poor questions than no answers at all - It would make some users even more afraid to leave the safety of the comments for the glory of the answer box.
If anything, new users are quickly scalded for the manner in which they ask a question and begin to understand etiquette and the most constructive way of asking a question (sadly not all of them!).
This is nothing but a personal view - but it's good to see experienced users attempt to educate as far as possible - an example of which I saw today by a user with 34K+ rep, only to be pwnd by someone in the comments giving the one-line answer. I'm more in favour of closure if they aren't of wider use.