I'm sure Mitt wants us to see this as his desire for selfless service to the country, but in a field populated with independently wealthy candidates, it's obvious they aren't in this for the paycheck. The thrill of power alone would be enough for many, but when a corporate candidate's primary concerns are deregulation of industry, curbing consumer lawsuits, and repealing investment taxes (as well as the "death tax"), it's hard to believe he hasn't looked at the bottom line.
The sad fact is that $400,000 is chump change for these guys. They're able to make much more money simply by changing the tax code.
Case in point: Dick Cheney, who in 2005 alone is reported to have saved almost $1.1 million due to the administration's tax cuts. That's more than 5 times his government salary. And he gets similar savings every year as long as those cuts remain in place.
This is also true for the rest of the CEO cabinet:
[from The Nation, 2001]: For instance, two retired CEOs, Dick Cheney and Treasury Secretary Paul O'Neill, would have reaped a combined $4.9-$5.2 million if the tax cut had been in effect last year, largely because of the considerable parachute payments they received by leaving Halliburton and Alcoa, respectively. Defense Secretary Donald Rumsfeld, who has amassed a fortune with the help of prominent Republican campaign contributors, would have added between $590,000 and $890,000 to his take-home pay--more than three and a half times his $161,200 salary as a member of the Cabinet.