I just watched a video interview with Bill Gates yesterday and he said that we're now behind in software. The entire robotics industry (according to Gates) is behind not because of hardware, but because we don't have the software. He went on to say that software will continue to be a field where we need even more people involved, where we have most of the hardware we need.
Plus, a reasonable fraction of the academic positions are purely teaching.
http://www.ams.org/employment/2007Survey-DG.pdf
I know physics is similar.
Actuaries, quant finance (it's not dead yet), crypto-related programming, logistics... there are lots of non-academic jobs (most of which pay better than all but the best academic appointments). It may be the case that giving up four years of earnings is not worth it from a purely pecuniary standpoint, but I seriously doubt that there is an overabundance of math PhDs given the jobs they can take.
The private sector is, of course, much less visible than academia.
A math PhD in an actuarial setting is out of place, like a CD grad working at Geek Squad (a hypothetical Geek Squad with pay comparable to programming).
While having the degree helps you get the job ("omfg you have a PhD you must be so smart!"), it isn't necessary. The number of jobs where PhD level mathematical knowledge is necessary is actually quite small. Producing more PhDs will probably not be as helpful jmtame seems to think.
http://philip.greenspun.com/careers/
Also that's kinda nonsense; what's really lacking in robotics is a suitable power source.
"Into the Eye of the Storm -- Assessing the Evidence on Science and Engineering Education, Quality, and Workforce Demand"
http://www.urban.org/publications/411562.html
Abstract:
"Recent policy reports claim the United States is falling behind other nations in science and math education and graduating insufficient numbers of scientists and engineers. Review of the evidence and analysis of actual graduation rates and workforce needs does not find support for these claims. U.S. student performance rankings are comparable to other leading nations and colleges graduate far more scientists and engineers than are hired each year. Instead, the evidence suggests targeted education improvements are needed for the lowest performers and demand-side factors may be insufficient to attract qualified college graduates."
Meanwhile, try finding a plumber or an electrician... Our physical infrastructure is quite literally crumbling around us while our heads are in the clouds.