When was the convential 6% (3% buyers agent, 3% sellers agent) real
estate commission establised?  What factors influenced the decision to
set the national standard at 6%?

The commision is negotiable.  There are companies that charge less. 
The national standard isn't 6% it is whatever the real estate agent
can convince you is the "standard".  Some try to tell you the new
standard is 7%.  If realestate is selling well in your area then
negotiate a lower comission with the rel estate agent.

There is currently a restraint of trade and collusion case in Kansas
(I think) by the FTC because some local Real Estate agents were
preventing other agents from charging a lower comission.

Remember the real estate agent works for them self not for the buy or
the seller.  They don't have sufficient incentive to squeeze every
last dollar out of the sale. (the agent gets maybe 1.5 % for the sale
so on a $10,000 price hike it is only $150.  Not worth it to them to
push for $10,000 more in price hike.)