Ask your self this. What propertys of a synthetic oil do not lend themselves to breaking a engine in?
Of coarse this is all moot as it fine to break in a engine on synthetic. The main thing is to not baby the engine during break in, regardless of what oil you use.
If the cylinders where indeed honed to a finer surface finish break in would take longer and be harder to achieve. You would think if the optimized the cylinder finish for break in with synthetic oil it would be coarser.I would not be surprised if the rings and cylinder honing were to finer tolerances on those cars.
Of coarse this is all moot as it fine to break in a engine on synthetic. The main thing is to not baby the engine during break in, regardless of what oil you use.