Minefield, this sizing business.
I think it depends on the garment and how it is intended to fit.
Our one-button jacket -- we make it so that, when buttoned, it is pulled together somewhat at the waist and lower chest. In this scenario, a 38" body chest would want a 38" garment, give or take a quarter-inch here and there. Any larger and, when buttoned, it will hang straight, without the intended "nipped-in" shape.
But with a raincoat, say, or a trench, we want at least an extra couple of inches in the chest, so that it is relaxed and comfortable, and may be worn over one or more other jackets in winter. You will see the pit measurement on our overcoats corresponds with this.
I know this is a traditional approach, but it seems in line with a fair few, though of course not all, brands. Every new garment development is fitted on a 38" bust, and fitted to fit, ummm ... right.
Hope that sort of answers your line of enquiry.
Edited by sehkelly - 7/16/14 at 2:58pm