Here's some good news for readers in Mexico. Reports are coming in today that Google Play Books has expanded into Mexico.
I haven't found an announcement from Google, but Google's support pages confirms the news. It also indicate that the expansion includes only Mexico but not the rest of Spanish speaking Latin America and South America. Portuguese-speaking Brazil, of course, gained access to Google Play back in December 2012.
This is a rather odd move on the part of Google. I would have expected them to follow in the footsteps of Apple and expand access to include all of the Spanish-speaking countries in the Americas.