Good comment above about car 'non oem parts'. Do people list replacement - wiper blades, exhaust systems, other brand tyres, air filters, batteries, roof racks etc etc? Of course not. So why the big deal about bike parts? I can understand anything that increases bhp like some exhausts, but why suspension, heated grips, luggage racks etc? Most of them are put on to increase safety.
It's just an excuse to up the premium. Always retain the original parts and swap back in the event of an accident.