I think Laurent makes a very good point about whether a vehicle has been repainted or the colour is original. Below are Bovintgon's Mk IV and Tiger I before they were 'restored'. There is really very little 'chipping' on either of them, but there is a huge amount of stains and wear on both (particularly the M IV, I love this photo).
You rarely see 'weathering' for what it's supposed to be, environmental impact. So often you can see wear and exposed metal on a model where it has no rational reason to be. The underside of the mantlet just isn't going to see that much traffic!
Also consider that both of these vehicles have had countless people crawling all over them for 50 odd years. Both photos are from 'German Tanks of World War II in Color'.
Below is two photo from an original 2cm Flak 38 that has had fairly limited traffic since the war. The first photo is the top of the elevation housing which consists of steel and aluminium construction. This weapon was repainted before going to Africa as evidenced by the second picture. You can clearly see, that even in the high impact areas such as the hand wheel, the paint has flaked more than rubbed away.
It really just needs more consideration towards each individual aspect of a model, as to it's material, function, location etc. rather than making it look like the only runner the Germans had to set against the Russians at Kursk.
Allan