I understand that piston uppers keep some of the powder residue out of the receiver but why is this so important?

Is this just an issue with FA and high ammo consumption users? I just use my AR at the range and sometimes critter control and never had any problems in function because of fouling. Is this because my AR never gets very hot?

Would piston systems be harder to make accurate? I don't mean just tactical accuracy but varmint accuracy?

Regards,
Mild Bill

Doesnt sound like you need it.  It will not make your gun a better critter hunter, or more accurate.  That having been said, I dont "need" a lot of the kit I have.  You wouldnt be the first to buy one just cause it is a better system.

The pistons really shine when it comes to service life, short barrels, suppressors, and they offer a bit of a performance advantage in recoil, muzzle rise and quick clean up.  The offer a bit more consistency as far as operating the action.  They are a bit more efficient allowing the use of a broader spectrum of ammo, eg. they can cycle subsonic (not sure if all do) and heavy bullet and hot loads with no change in rate of fire.

They have been proven not to affect accuracy good or bad.  AN AR WITH A GAS PISTON SYSTEM IS STILL IN LINE OPERATION.

I have had regular ARs over the years, and I have never had a problem with them for the amount of shooting I do, and I manage to keep them clean enough.  So for most of us, it comes down to having gear you probably could live without.  That said, many anti-gunners would find we don't need AR's at all.  

I have a theory that the piston does not offer much to a standard barrel length AR or M16 for most guys.  A varmint guy would likely want a full length barrel.  If the thing were to get plenty filthy on a regular basis, I would suggest the piston AR would offer an advantage.  I wonder if those maintence guys who were ambushed in Iraq and did not have properly maintained weapons would have reaped the bennies of the piston systems.  If that was the case, they just would have been waxed instead of taken prisioner, so I suppose it worked out for em.