LOL, I was thinking the same thing (in regard to charge distance).
Anyway, in response to the Cabbage - read asian avatars post, or my post from the first page. There is a clear reason for including the rule - mixed initiative combat. I used an IC in my example, but it could just as easily be a squad member with a higher initiative.
Basically, the rule states that you are locked into fighting whomever you were in base contact with before blows were struck. As my post from page 1 shows, if you are in B2B with an enemy, but that enemy was eliminated (and you are no longer in base contact with any others) you CANNOT allocate your attacks as per the 2" rule if they are going to a different unit than you were originally in B2B with.
This can and will come up whenever you have mixed initiative combat (SM terminator squad, Eldar squad with an exarch, or any two squads with differing I attacking someone else).
It was explained clearly several times, there shouldn't be any contention at this point.