SkyCop - the nice gentlemen of the CAA allowed the military men to do the 1179 on the mil machines so you wouldn't have to break into your pension funds to finance it! In other words, a concession. or.....
Perhaps it is because they are so close to the SA341 as to make no difference - in the same way that the Bell 206 "JetRanger" 1179 allows you to fly the 206L "LongRanger" which has larger engine, larger cabin, larger blades, 2 more seats blahdy blahdy...
Now, what would be the chances of a civvy being allowed to do an SA341 rating in a mil machine????? Don't bother answering that one!!
As regards other differences, one obvious one is that civvy Gazelles have tail rotor drive shaft covers. I also thought the mils had larger blades, but I may be wrong on that one. And, if they have more power from the engine, wouldn't that have necessitated a larger (stronger) gearbox as engine output is usually restricted by the torque the g/box can handle?