I believe it was for PVP purposes and the fact that sometimes even after several minutes has passed since the heavy drop, some people are still running around with machine gun ammo effectively using it as a primary.
The counter to this argument is that in the D2 beta, the fusion rifle gets six shots after picking up power ammo effectively making it the new "machine gun" of D2 so to speak.
Thoughts?
[i]~Nyahh! =^,.,^=[/i]
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I think maybe they're trying to make "power weapons" all one-hit-kill, maybe? Machine guns really don't have a place in that scheme, I guess. Fusion rifles, shotguns, sniper rifles, rockets, and even the grenade launcher all have the potential of a kill from a single hit. The best machine guns in D1 required multiple hits to kill. Just my guess. But yeah, they don't want people roaming around with all that destructive power for so long, I guess.