I think on the old board, threads were automatically locked after a certain period of time. I think it was at least 6 months (but not really sure), which I'm still comfortable with. So I think perhaps the main part of your argument had been addressed before, just isn't at this time since we switched boards. So unless there is a technical reason for not locking the really old threads then I'd support that.
However, I saw your other thread on this issue in Software and I am not quite sold yet on the marking as solved or inactive. I certainly think your suggestion of locking the thread after 1 week is far too short, 1 month may be too short too. But I do understand the argument you made about help perhaps being outdated. Outdated help becomes outdated far faster in your malware world though than typical software. Sometimes, particularly with MS Office software, or really any pay for software, the advice may never become out of date because the advice would be version specific. I know some people that still use Office 2007 because 2010 wasn't worth the expenditure to them.
I might be able to get onboard with 'inactive', but at this time I am not seeing the benefit to that.
For an example where a thread almost a year old, but the advice hasn't changed:
External ard drive not showing up on my Macbook Pro
In fact, there is another thread where the same stuff is discussed from Jan 2012:
External hard drive won't show up on my Macbook
The second one (January) kind of drug on to more specific advice, but the first one has had 3 people bump it with the exact same problem. I've given them the same advice each time (or at least didn't change my advice since it was already given earlier in the thread), and all 3 that bumped it never replied back. If we made each inactive after some period of time I'm not sure that helps anything. And it makes search results return several threads all of which are worthless to someone with the same problem. At least now if someone replies it got fixed, all 3 (4 counting OP) 'problems' are fixed in 1 thread.