Like everything in life I guess its not a hard and fast rule. Single answers per person are recommended because it avoids discussion. The emphasis is to try and get people to update their first answer with any new information or thought or even responses to comments.
This is not traditionally the way people did it, instead they would post another 'answer' in a threaded discussion. The One answer per person policy was adopted to try to prevent threading.
If you truly have 2 separate but equally valid answers to a question I'm sure no-one will mind you posting twice.
