For the PRI, buying votes isn't just an electoral manipulation; it's an essential part of their character. Giving voters gifts is part of the populism and clientelism that allowed the party to institutionalize their revolution. It's a basic political-economic transaction that they've done for generations.
However, for all their talk about living in a new, more democratic era, the PRI seem genuinely surprised that anyone is criticizing them for their vote buying schemes. That's never happened before, at least to the extent that it is today. They seem unsure how to react because, for them, what occurred was a completely normal action that they've done in every election. It's been allowed previously, even if it wasn't democratic or legal, and nobody warned them that they would be judged for it this time.
The hemisphere has been caught off guard too. I think every government across the political spectrum from Chile to Venezuela has recognized the legitimacy of Peña Nieto's election win. For a hemisphere that constantly argues over the rights, norms and violations of democracy and fair elections, the legitimacy of the PRI's election win in Mexico hasn't actually been questioned by any government. Whether governments hope to have good relations with Mexico, think that EPN's margin of victory was too big to be invalidated, or simply don't have time to care, the international community has gone out of its way to minimize the scandal. There is a banality about the PRI's vote buying that wouldn't be as easily accepted in other countries south or north.
Most of the hemisphere's governments, along with the PRI, assume these questions about the PRI vote buying are just temporary. They think the legal challenges are going to be whitewashed and the protesters are going to lose momentum. It's up to the pro-democracy movements in Mexico, including the students who are part of #YoSoy132, to prove them wrong.