There are two issues at play here, and deserve two different meta questions (so I will break then into separate answers - other answer here).
The second question is more unique to SFSE:
As Salesforce continues to develop, it eliminates older versions. Are questions still valid if they are based on the limitations that are no longer limitations (or features that are no longer features)?
My opinion on the second question is to neither close nor delete these questions, but to provide useful answers that are now obvious.
First, it would be a burden on the community, and doing it half-way would create a set of expectations that we cannot live up to.
Second, I think that old information is actually useful. Off the top of my head I can think of three distinct use cases for old information.
- When you're going through your org and trying to figure out why the previous admin/dev made the choices they made. But there's not a lot of advantage there.
- More important is when you are maintaining ancient Apex or VF code from, e.g., v16.0, and want to know about a particular undocumented bug/quirk or a workaround.
- Also, many "old" features in SFDC are deprecated but not removed from orgs that are already using them (like S-Controls).