I would add that the demand for may differ between different branches of math. For example, I would suspect (although I don't have the data on hand to back this up) that there is a greater demand in academia for those with a background in applied math than those who specialized in pure math (particularly those with a background in computational math, optimization or probability).
Related to this is the overall greater demand for economists, statisticians, industrial engineers/operations researchers and computer scientists in academia (since all four fields are heavy users of math, and it is not unheard of for applied math PhDs to find themselves pursuing research in any of these fields).