An e-mail from an acquaintance south of the border includes the following:
"Information is confusing and not helping at all. If we extrapolate the (real) cases we know of and the information we are getting it does not make sense. We should have more cases registered."
That fits with what I've been guessing: The only way to reconcile the apparent lethality of the swine flu outbreak in Mexico with the lack of same outside the borders is if there are a lot more unreported minor cases in Mexico. The official Mexican statistics suggest a 1/10 fatality rate, but they seem to be based on patients who present themselves at hospitals or other medical facilities, as opposed to those who spend a miserable few days stuck at home. Otherwise, you've got to believe the virus somehow magically becomes less virulent when it crosses the border.
On the good side, that suggests an actual mortality rate much less than 1/10. On the bad side, it also suggests there's a much larger disease pool in Mexico than reported, with correspondingly lower changes of controlling its spread - if those chances ever existed.