You may be right. I don’t do many short story mags or anthologies, and the one’s I’ve done, I’ve had no problem with the rights they’ve asked for. I’m usually doing it for a charity of some sort. Like Unfettered which raised money to pay off Shawn Speakman’s medical debts.
When the publisher gives a listing to Amazon they indicate what markets it can be sold in. If they, for instance don’g have UK rights, that checkbox is left blank. Sometimes you’ll get an email from a reader saying something like, "Hey why can’t I buy your ebook in Singabpore? And it’s because someone forgot to check the box for that market. Usually it means an email to the publisher who checks the box and then the book magically appears in the store when the person logs in from an IP address in that country.
I should note that some people use programs to change there IP so it looks like they are in a different country than they are. And so some people, for instance, will buy a book that’s not available in their country. Not technically “legal” but at least they are paying for it rather than pirating it.