As to the two-bolt cheap Stihl vs.1-bolt absurdly expensive Stihl - I don't have a clue and really don't care. Doesn't have much to do with the OP's original question.
If 1-bolt vs. 2-bolt isn't important, why did you bring it up in the first place? You must have thought it had some bearing on the topic, else you wouldn't have mentioned it.
(The answer to the question: because when you insert bolts into a plastic housing, you're gonna need 2 of 'em. If you locate them in metal, for that displacement class you only need 1. In other words, Brad speaketh wisdom about clamshell saws.)