I would imagine it's based on historical consistencies as well as the plane's design.
B29s and A6Ms catch fire easily, just like most of the historical data and based on design flaws.
A20 is tougher than the 110 because it was designed to hold more stress, it had to haul 8x 500lb bombs around. And I'm sure it had armor added as well, where as the 110 was supposed to be a long range escort at first, so less armor for less weight/more range.
There are some quirks in AH though, 190D's glass radiator, P47N losing their main fuel hit all the time, etc etc.