It's not poop, it's fact boys! 
You have to run a pump faster & with a higher pressure setting (which both combined would represent it working "harder") with 6mm hose than 8mm to achieve a set flow rate. 
However, the pumps are up to the job with either hose but reflecting the above fact, with 6mm you'll use more battery power & have more pressure in the system- which is why you see posts with no end of leaks, connectors popping of etc etc. 
It might be true what your saying winpro but I GET PLENTY ENOUGH OUT OF MY BRUSH HEAD EVEN WHEN I WANT TO CRANK IT UP (sorry just seen caps) with wide fans on for fascias etc. no leaks, and my battery lasts over a week on one charge...all i need my friend 
You'll still get enough flow mi old mucka

but if you used 8mm you'd get that same flow with the pump running slower & with less pressure, there are benefits which come with this.

That's my main point.
As for pump durability, I think most pumps are well capable of both 6mm & 8mm hose & for how cheap pumps are I don't think it's a very valid argument.