Yes, answers to Questions should be in Answers, but when the issue is something trivial like a Python syntax error, it hardly seems worth the effort to put down the phone, find a desktop and provide a true Answer, especially when the Question could be (justifiably) closed as off-topic before I could hit the "Post Your Answer" button.
There are plenty of times each day when I have time to scan for interesting problems, but there are fewer opportunities to spend 40+ minutes constructing and testing an Answer. The way I see it, if a 1-sentence comment can solve a Question, then it isn't much of a question, and it's not really worth the effort of a formal answer.
I've been encouraged to convert a comment to an answer on occasion, but haven't on all of the opportunities because of the time investment required. I admit that the older ones, especially for users who haven't been logged in for more than a year, seem like throwing good money after bad.
The maximum size on comments has grown significantly in the 3-1/2 years I've been a member, but it's still not large enough to house a proper Answer, so I'm not worried that comments are going to replace answers. (In fact, the response previous to this sentence was deemed "too long by 669 characters" to be a comment, which kind-of proves my point.)