Actually I'm really glad you've mentioned it. I've long wanted to explain myself but the opportunity has never arisen before.
Basically, it makes it easier for people, especially those with less than 20/20 vision, to easily differentiate between their introduction, wordplay and the actual answer.
So often I've been trying to help a poster with a query, but when I read it, I have no idea where the clue starts and ends. For example, there might be an explanation as to why the question is being asked but then there's no punctuation or numbering to indicate ' right, now here is the clue.
So, I decided long ago to try and make my replies as clear as possible, at least as much as I could - hence capital letters for answers.
However, if it's annoying people I'm happy to think of another way.