No offense, but all those excuses feel quite ..constructed. The reason advies can't emigrate is for OOC purposes, I assume. It's just one of the drawbacks of choosing the class.
A small, but very important, portion of the commoner aristocrats were the large merchants and bankers. While nobles and senior clergy often got involved in lending money, it was the commoners who did most of it. These pools of money were essential for economic growth. All manner of capital improvements, from ship building to industrial expansion, required a large amount of cash to get started. The nobles tended to spend their capital on building splendid homes and fortifications. The church pured much money into cathedrals and abbeys. But vital items like iron works, cloth factories and merchant ship fleets were largely built by entrepenurial commoners. These items produced more wealth, where castles and cathedrals did not. Eventually, this mass of commoner wealth turned into political power and this was beginning to happen even during the Medieval period.
http://www.hyw.com/books/history/Aristocr.htm (I'd look for a better source, but I have an exam in 4 hours 
In the same way we assume the Nobles to be the very cream of nobility, with even the most basic knight far above average nobility, we probably need to assume Adventurers are far above peasants and the regular commoner. With sometimes enough money to outrank Lords and armour worth huge amounts of money, many Advies concentrate more wealth than many nobles.
I also think that we are pushing the boundaries of our Medieval apartheid too far. Many nobles will have been very pragmatic towards common people, certainly to those with power and money. I can hardly believe Jakob Fugger or Pieter Bladelin were unable to buy a boat, let alone kept from booking a passage.
It's fine tht Advies cannot travel, for some OOC reason. But please don't make up IG excuses for it?
Would you expect that Jakob Fugger or Pieter Bladelin could be arrested or beaten on a noble whim as we can with Advies. Advies are not of the merchant class, they are of the true peasant class from all appearances. There is vast social difference between the common people and the peasants, with the peasantry being a sub class of the commoners, though depending on the time and place it was somewhat possible to move between the sub classes.
We had similar discussion to this a few months back, that covered all sorts of things like the possible scarcity of ship travel blah blah blah and a more recent one here
http://forum.battlemaster.org/index.php/topic,700.msg12804.html . It is often brought up as so far as I know the devs have no intention of adding it.
