As it turns out, you cannot sort on number fields either.
I ended up creating my own class that defines all of the fields as the data type they are suppose to be. I am then able to do with them as I wish. Dates sort as they should (by year, month, day instead of by month).
If you put a stop in your code just after the query finishes and look at the results, you will see that the results are a dictionary with either strings or numbers. It doesn't maintain the data types even as they are defined in the web service. Seems crazy to me.
After defining these fields, it does add just a little bit of time to process, which seems a bit needless. I'm hoping ESRI can fix this in a future version.
Dorothy