And as noted elsewhere, they have different ISBNs than the US editions, so if a seller send and int'l edition when you ordered a US edition, they did not send the book you ordered and the ISBN discrepancy proves that, so you should return it and complain to Amazon.
It would be even worse if customers in the poorer market only had access to products they can't afford. The important thing IMHO is that the lower quality version also has a lower price, and that, in case of re-import, there's a way for customers to know.
So, while arbitrary these barriers have the place till we have movement of people.
I did this with math textbooks in college. You can buy "gray market" books, which are versions made for foreign markets but bought by resellers and reimported to the US. They're the same exact book, but printed without color, on cheap paper in a cheap binding. This was perfect for me, since they were also much cheaper than the US edition.
If anything, the discrimination was going the other way. The only way to get a cheap copy of the book was to buy it off the gray market- the punisher wouldn't sell the cheap editions inside the US.