Facts about the functioning of laws/regulations are always important even when some some aspects of the body law applicable result in benefits or disadvantages for a minority, for a majority or for both.
"Exceptions" aren't exceptions when the "exceptions" are part of the applicable body law. The "general rule" is only a general rule when "exceptions" aren't part of the law/regulations applicable.
The last sentence in the post above is also far from being generally true in the world. Some countries can exclude and even may exclude, from entry and/or travel, some citizens of their own country. Many countries have a legal obligation to grant admission to some kinds of foreign citizens. The US, Canada and Mexico also have legal obligations to provide entry to citizens of the country across the border who happen to be members of some Native American tribes with ties in the neighboring country. These people are not exceptions -- these are people who travel under the rule of law without legally requiring a waiver to enter the country despite not being a citizen of the other country. Most countries have a legal obligation to not make their own citizens stateless, which is why refusing entry to their own citizens is not usually lawfully permissible and people make general statements like in the above post that are not generally true. Most countries -- not all the same ones as those covered by the sentence before -- have a legal obligation to not deny admission to some foreign citizens too.