Ah, but why did Shermans get that reputation? Because they used petrol engines? So did the Germans and they don't get this trait. Oh hell, not even the Panther got the "burns easily" and they caught fire without anyone shooting at it!
Besides, these are tanks loaded to the brim with explosives and the fuel, in the safest area of the tank, is supposed to be that big a factor? Hmmm, that doesn't seem likely.
I'm of the strong belief that there wasn't all that much in the design of the Sherman that made it catch fire any easier then other tanks. IMO it's a case of fairly weak armour meeting up with the potent guns of the Germans. Even the 75L48 is a pretty bad ass gun.
Germans typically had better armour going up against weak Allied guns. So no wonder that they enjoyed a better reputation. But the moment German tanks got shot at with decent guns, they went *woosh* too.
Shermans brewing up should be the natural result of armour v gun, not some magical +2 bonus to catching fire.