There's no policy, but as Patrix points out (and its especially relevant when you read the question title standalone which just asks "What software do people use" indicating the lack of an official one as a side note in effect during the question) the information that an official client is available has been included and is currently the highest voted answer, and the OP has been informed by other regular users to perhaps change his accepted answer.
That's where things get tricky. With some subjects, things get out of date real quick. And this is one of those. Personally the preferred solution for me personally was if the person providing the new answer when the official client came out just didn't answer - it wasn't an active question at that time being 3 years old but now there is a fresh answer it becomes active, and now becomes a sort of Zombie question brought back to life due to new information. In the perfect world, this old question would not have been resurrected for me, but when they are, we have to try to tread the line between updating the question to make it relevant, which risks making existing answers and votes irrelevant.
A tough one.