Io's uniform temperature distribution
Another idea being kicked around by the Io community at the Jupiter Conference, being held this week at the University of Colorado LASP in Boulder:
http://lasp.colorado.edu/jupiter/
is that the uniform temperature of the surface, as indicated by the recent Galileo's PPR results, is due to wholescale, extremely recent, volcanic resurfacing. As others have noted, latitudinal differences in solar insolation at these distances in neglible. An endogenic source, undoubtedly related to Io's volcanology, is almost a certainty.
Alex R. Blackwell
University of Hawaii