I believe edge17 means changing the exercises for the cheaper global edition, so students in western markets are forced to buy the expensive version as they may be assigned these end of chapter problem sets.

Yup, protecting in that the majority of the revenue for the publishers comes from the western markets (US/Europe).

It's the same reason companies like Apple don't sell less expensive phones less affluent markets - if they did the price spread would create an opportunity for arbitrageurs. Google et al however, does create less expensive alternative versions of their products for other markets.