There is nothing wrong with synthetic during break in. Many cars on the road, including Benzes, Porches, etc come with Mobil One from the factory. It _may_ have _used_ to be an issue in the olden days of cars, but it certainly isn't now.
However, the part about not switching to synthetic (if you weren't already running synthetic) after 75k miles or so has some validity. Synthetic can get to (and through) places that regular oil can't.
'01 Spectra Blue