Thanks to all for the reply's
I actually like using standard ammo from time to time - I like the knockdown effect from it.
I understand that it might not be the best min/max option but I play more for fun than anything.
The thing is - I don't see this with any of the other Dual Pistol powers - where Standard ammo still does comparative damage to the rest (albeit on a more commonly resisted damage type)
I agree it is a strange choice - but I guess I'll have to live with it