The problem is that answers should not be posted as comments. These "non answers" discourage others from posting the same information as a proper answer and the information cannot be voted on or accepted. The question remains, essentially, "unanswered."
This is becoming increasingly common on many of the newer sites and it should be discouraged, not rewarded (by moving the comment to an answer).
In practical terms, I would like to see the answer properly posted. I try and encourage these users to re-post their comments as answers, but failing that, someone really should take it upon themselves to use the information to provide a proper answer. When comment-ers see their information usurped, it might stop the behavior the next time around.