This is really interesting, thanks.
I don't know if personal information can be seen as a property (of course not) but, isn't it?
Of course, I agree with the point of poloniex just taking care of its own back, for they can be accused of many stuff. But, in every contract, when policies change, one of the implied parts should have the freedom to disagree and stop the commercial relationship at that very moment.
The property, in this case, is your money, which you no longer are able to use due to the change in their policies. Maybe this is not an extortion, but what is it then?
Just wondering, I don't totally understand how if a contract changes in its policies you are not able to say no and withdraw your funds, as well as stop all the relationship.
I feel that question has not been answered yet.