Um, careful, 3" pipe flanges and lower (150 or 125 lb. rating) also use four bolts.
SAE flanges are for hydraulic equipment.
Taking a step or two back, my opinion is that "standards" are created to provide a relatively non-changing reference design, so that parts can be interchanged between different manufacturers; also, there is an implied intent that the design not change radically over time. It's a bit peeving to me that a pipe flange, whose basic design has not changed in more than 70 years, has a "standard" that keeps being "updated" on a <10 year cycle. Seems a bit like a stockbroker churning an account.