I'll have to go with @rolfl's answer instead of @200_success's. While saying '[initial code authorship is only part of the software lifecycle][1]' is a very nice idealism*, code refactoring by current code maintainers of the posted code here can't possibly depend on newer answers to the original question years on. I would imagine that the current code maintainers ought to have posted their own questions, or explored newer and better solutions by themselves in the future.

*Very hypothetically speaking*, if we have helped someone solve the Y2K problem here (handle `YYYY` instead of `YY`), should we allow new answers to solve the Y10K bug (handle `YYYYY` instead of `YYYY`) down the road?

Therefore, I think we should naturally let questions 'retire', and if we do come across *way-too-helpful* answers on ages-old questions suggesting new features that are not available originally, perhaps an edit remarking so should do it.

\* - This reminds me of [coding for violent psychopaths][2], but that's another story...

[1]: http://meta.codereview.stackexchange.com/a/2174/27975
[2]: http://blog.codinghorror.com/coding-for-violent-psychopaths/