If there's an international limit of 5000 mAh as to sending LiPo battries on a plane, then that's a good argument. Someone better find out!
I've heard that in essense you're not really allowed to send LiPo batteries with air freight at all (ground shipping only). Some webshops cannot sell to other countries due to this. Also this has to be investigated thoroughly.
In practise I can't really see the airlines opening up your luggage and checking the mAh rating... I think this is a VERY theoretical problem if any. (Hand luggage would be worse of course).
Does this mean laptops will never come with batteries with more than 5000 mAh???
An argument against size restrictions is that manufacturers won't try to make thinner cases, wires, smaller solder tabs etc... to try and shrink'em... safety first!
And as to size restrictions for NiMH cells... how often have you seen a stickpack being dismantled and measured? Tabs soldered off so you can accurately measure the length? With metal calipers shorting the cell...
It's way over complicated if you ask me... Not to forget... if the text on the shrinkwrap is written in the wrong colour, wrong colour on the ring etc... they're not legal... hence you're always insecure when ordering new cells...
At least for OR... why do we need any battery rules nowadays at all? Nobody's dumping... nobody can go faster with more power...