I think that this shows that there is a different level of what we each find safe when it comes to filled tanks. The issue is if the US law states that this isn't safe then that is what the law is.
The one time use containers for pumps are not in the same level of a safety concern, they contain much small amounts and if they did go off (even though I assume to be able to be sold and transported that they have long met these requirements) the damage which could be done is much smaller than with a larger sized tank.
I know that propane has to be transported standing up and fully secured.
Saying that it is okay to ship tanks full is the same type of thinking as saying that there is no need to re-hyrdo your tanks once they are out of date.
I have seen the results of tanks that have blown up, extensive burns to people/clothes and if it is done while some random person is handling or moving a box there could be a huge amount of public outcry against the sport of paintball.
Better to be safe than to be sorry.