Actually, this is a bad example to try and show that 4E (specifically) doesn't make sense. It may be that D&D doesn't make sense for double weapons, but this particular issue spans across 3.X and 4E. I'm not sure if CovertOps's 20-year RPG veterans account for this. i.e. if the one guy who left was a 3.x veteran, he not only wouldn't have made the mistake, he would've been surprised that an issue could've possibly existed.
The difference I think is that in 3e if you had a weapon that did extra damage per swing you would apply it to every swing. Double weapons have their own rules in 4e and they diverge from how they worked in 3e in this regard IIRC.
Saying that someone is a 3e veteren and therefore would not make a mistake is disingenuous. People make mistakes all the time no matter who they are. What I was trying to point out is that 4e has specific rules on double weapons in PHB2 that interact with magic item properties and daily powers and that if you don't read them you wind up with his position of reading the magic item "Property" and coming to the conclusion that the damage applies to every attack which in his case wasn't true. It would be kind of like looking at the movement rules to see you can spend a move action to "Shift" one square and not consulting the rules on shifting to see if there are any limitations like not shifting while prone or through difficult terrain.
Exception based design is what gives us this "layered" rules set which I think is what makes this rule set so much more complex than previous editions. It is both the boon and bane of our existence.