I question the statement " one million expats live in Mexico" San Miguel 12,000, Lake Chapala 20,000 , PV, Cabo, Meridia, Cancun, Playa, etc. if one were to add the other common areas in Mexico where most expats live you might be hard pressed to find more than a dozen at most, and each area having much, lower expat populations than Lake Chapala and San Miguel.
I have heard it said the the Mexican Gov. has not kept accurate records of all tourists and others, that return the US and Canada. It may be a marketing ploy on Mexico's part to say, "One million expats live in Mexico" "Come on in the water's fine" as the Mexican Gov. freely acknowledges the benefits from expat $ to Mexico's economy. This is of course just my opinion, but I do find it difficult to believe "one million expats living in Mexico".