I'd be interested to know the reasoning behind it at least, as I'm sure there was a good discussion about it. It's strikes my curiosity is all. I look at some of the weapons and barring choosing them for flavor don't see why they would be taken over others.
The only reason I see for the warhammer, for example, is that it works well against undead - skeletons in particular, which are unaffected by critical strikes. By making it 2d4 instead of 1d8 you're making it even more so a weapon of choice against them and trading it off with a lower crit multiplier so that it's even more so a specialized weapon.
that or the fact that it would otherwise be identical to the battleaxe, or perhaps a combination of both!
Again I'm just curious, I'm not looking to have anything changed