Don't know, and I don't know whether they are actually more serious than the ~20 reported cases in the US. I haven't seen an analysis of the cases in Mexico, but a few factors to remember:

- reporting. In Mexico you may see fatalities reported more accurately than cases of swine flu. The top level impression from US media is 100% of those infected in Mexico have died from this flu strain, when in all probability there are a number of un- or under-reported cases of swine flu, of which the reported fatalities are a smaller fraction.
- treatment. Basical health can be sketchy, not everyone can get adequate basic treatment for the flu.
- its a small sample set, but this flu seems more serious in younger folks. Very young quite often can't complain or show serious symptoms until the flu is relatively advanced.

Take heart from the reports on US infections, this seems treatable at home with basic flu treatments.