If an answer is for one and only one version of Ubuntu and that solution doesn't work anymoredoesn't work anymore in recent versions, I don't see why it should stay. Now, generic questions and answer can stay. Just edit out the versions or add a title that reads:
This only works from 13.04 onwards
For example, if the answer has/needs different instructions for some version of Ubuntu. If some instruction is only for a EOLed version (say 11.10) verify that it doesn't work anymore, correct if it's salvageable or edit out if it's useless.