The biggest difference is the role of ICANN and their willingness to regulate the management of a TLD. With ccTLD they have an official policy to be hands off and not dictate what a country will do with their top level domain. If the US government would start to mess with Verisign and how the registry handles domain, then ICANN is within their own policy to just move it somewhere else.

The government of Montenegro could, just like many other ccTLD, decide tomorrow that every registrant must be a citizen of Montenegro. Many countries do this today, and it is no big deal because it is the country of and ccTLD that dictate how their domains should be operated. They can raise prices by a factor of 100 if they wanted, decide on some form of ID for registration, or dictate that you must have a company located in the country. ICANN has no objection to any of that.