I was curious about why the paint is so often depicted as coming off on the Zeros. Were the Japanese planes actually like that or is that a modeller's habit?

I hear that it wasnt so much that their paint was bad quality so much as it was their primer that wasnt up to snuff. Apparently early war planes were pretty immaculate. Typical quality control and sourcing issues arose later in the war. Extensive chipping is very prototype. Looks cool too. Iv sen that the airframe could be losing paint everywhere, and the groundcrews would touch up the Hinamarus alone.

I've heard one theory that it was because they didn't use any primer on some planes.

I have heard that too, and someone corrected me on it ...they said that it wasnt that they didnt use primer ,but that the primer they used wasnt very good. Im sure the boys on J-aircraft.com would know. Personally I dont know what to believe because I havent devoted time to actually studying the matter ....