I believe Finstersang is using Round to represent the entire combat round, and Turn to represent an individuals set of actions. If I have that backwards my use of the words will need reversing in this post.
A simple combat example, two participants - you, and opponent. In this case you go first.
When you go, you gain 2 Edge.
With Edge limited to 2 per Round, when your opponent goes it doesn't matter what you have or don't, what they do or don't, you can't gain any further Edge.
If Edge was limited per Turn, you would still have the chance to gain 2 more Edge - say if your AR is high enough and something else.