But the question is how old is old, there are threads like the one for the 3DMark 06 benchmark which people bump use whenever there's a result to post. Another example is the Naruto and Bleach thread in the general section, every Friday people post the link to the latest episode and have 5~6 posts related to the same and it goes down to the second or third page in between before its bumped up again the next week. Would you rather that there are separate threads each week/month/year rather than a single one. Other than that, there are the iPhone, PSP threads in which are used by people for their iPhone, PSP queries instead of creating a new one every time.
I would say closing old threads would be more trouble when compared to the odd newbie who bumps a old thread without a valid reason.