Couple of things about the break in process.
First, it's not a myth. All the metal components that rub against each other will need to slightly wear into each other due to manufacturing tolerances. Or in the case of piston rings, they need to "seat" in the cylinders. Those tolerances are really small but differences do exist.
Second, you're not dealing with just the engine. The biggest reason for the speed restriction to begin with is the rear end. The ring and pinion gears need to get aquainted... And they'll produce quite a bit of heat doing that. If you abuse that process, I don't think you'll break anything right away, but oil seals could fail later on and you might develop a howl in the rear end at certain speeds or conditions.
Third, the idea of varying the RPM is a good one for purposes of seating the rings in the engine, and generally trying to drive it like you intend to do most of the time is also a good idea. Don't be afraid to punch it once in a while either, just don't let it rev up too high during that first 500 miles.
Just my two cents based on past experience.