My thought is I don't want to be trying to stock up when somehting happens, I want as much stock as I can. Lets say I have room for 200 batteries, if I have to stock AA, AAA, 123, C, D then thats only a handful of each, but if I standardize on AA then I can stock 200 AA's.
Another thing is unregulated lights can utilize batteries which are too low to run in more complicated electronics. pop the "dead" battery from the radio and into the led light for a few more hours.