Don't you think that this discussion is pointless. Game mechanics is what it is and can't be changed. If you wish to crate special currency for all houses which is impossible and not necessary.
And if you need explanation for Gallic Credits that is simple. All transaction are based on nural-net transfer which was invented before great war between Alliance and Coalition. Now the system is still operating on both sides (Gallia and Sirius) and as perfect system it can easy exchange Sirius Credits to Gallic currency.
