I hope that I did point out something important, that the life of a
helmet may be limited by other factors.
the OP did say that
"5 years constant use, a few minor scrapes (there was that low tree
branch
once as I recall) so I guess I can't complain"

so manufactuers have said 5 yr max and then you need to factor in wear
accelerants(sp?)
but then again do you want to stretch the ability of a helmet to
effectively absorb impact force?