The change reads:
Page 66, Target Remains—Chargers Pull Back Add the following at the end of the final paragraph: “In any case, all chargers who charged the same facing must end up the same distance from the unit they charged.”
I am assuming that the inclusion is to stop the following situation:
Here you have three units combo-charge a wide defender. The Target remains and the three attackers must withdraw 1". By the inadvertent (or judicious) placement of a character behind A2, that unit is unable to retreat 1" and so the Defender does.
If the Defender is then boxed by its own units, its only target becomes A2.
A smart opponent could use the placement of his units and characters to ensure that any countercharge had to be directed to the highest Defence (or highest Nerve) target. It also allowed Thunderous Charge on units A1 and A3 to reset for future combats.
I asked on the forums last year whether this was intended and was told that it was legitimate (which is a slightly different thing). With our local group, I explained it to my opponents prior to a game so there wasn't a "gotcha" moment.
Personally I am glad to see it gone. I always felt it was an unintended consequence of the interaction of two rules. The problem was it could happen consciously or by accident but always felt a bit "gamey".
The FAQ clears it up by creating a same distance for all mechanic.