The "two triggers only" limit of ED makes it barely usable in practice: you have to bind 2 unrelated things on the same trigger. So you have to go through the "stage 1" action before being able to use the "stage 2" action (Which means "waste something", in most cases, usually weapon energy)
You'd think that would be useful for the Vulture in dual lasers, as you could fire either 1 or 2 lasers using the same button, without actually wasting a fire group, but even that is not possible (at least not without macros): each laser is bound to only one fire mode. So you'd need a macro mapping Stage 1 to button A, and Stage 2 to button A + B.
So... Not really useful in ED, unfortunately.
"Fairness" can't be the official answer, right? I mean, not seriously? There are so many differences already between using HOTAS/Head Tracker/<Name your device> vs using M/K or Joypad that, certainly, having 4 fire groups instead of 2 (Or, even better: Unlimited fire groups) would only be a detail compared to what already exists in terms of differences.