This may be a UK/US spec thing but the washers on my 2001 model are flat copper (rather than what I would call a crush washer which I would expect to find on an exhaust system).
It may equally be a terminology thing where in the US a flat copper washer is described as crush due to it's ability to deform a little when under pressure.
Assuming this is a terminology thing,then the reason for renewing is that copper "work hardens" & with repeated use can crack due to the afore mentioned hardening.
The internal & surface stresses caused by "work Hardening" can be relieved by heating the washer/gasket uniformly to bright cherry red & then either plunging into cold water or allowing to fully cool naturally,this will anneal it back to it's original soft condition.
A good way to ensure uniform heating is to lay the washer/gasket on a thin sheet of brass & heat the sheet from underneath,this method was shown to me many years ago by a clockmaker when I was trying to re-use a copper cylinder head gasket on my Triumph Bonneville.