Sorry I disagree, what if he finds something that could cause damage to the cylinder plating if left untreated? Thats a bloody expensive job especially if there is welding involved as well as replating! 90% of the bits? More like 40% when you take into account 2 barrels and 2 heads surely? They certainly dont make up 10% of the top end of the engine!

Changing a piston is part of the servicing, preventative maintenance. IE changing of worn parts to prevent further damage to more expensive items.

I always have stuck to this, whether while racing or road riding. rather change a £90 piston than pay £90 for a piston then £150 for cylinder repairs...

Or maybe nsr's are so magical they never wear out?