Well, the little I've learned of manufacturing over the years is that the $$$ wins every time when it comes to manufacturing costs. So far as slinging out internet theory's go, those magnesium pistons may be too costly for something that turned out to be a hit. So why not take the "new 362" we just made and slap a 400 tag on it and call it a day and sell the chit out of 'em.
I'll give one recent example to back up my thoughts on this...
A mere few days ago I got in a brandy new still in the box with all the paperwork and such MS201C rear handle saw. Which seems in appearance the same in all respects for one, the spark plug. These always came with NGK's installed and now have a Bosch plug made in Russia in its stead to save a few cents.
In other words, if the rest of the world is selling less for more, why not Stihl too?