Perhaps you missed it:

President Bush on Tuesday shut a loophole that defense contractors had been using to avoid paying millions of dollars in payroll taxes.

Bush signed into law the Heroes Earnings Assistance and Relief Tax Act, which provides tax relief for military families. Included in the legislation is a provision that would treat foreign subsidiaries of U.S. government contractors as American employers. That means they now have to pay the taxes that finance Social Security and Medicare programs.

Defense companies such as Combat Support Associates and KBR Inc. set up shell companies in the Cayman Islands and other tax havens to avoid paying those taxes on their American workers.

More about it here:

Included in the bill is a tax provision written by U.S. Sens. John F. Kerry, D-Mass., and Barack Obama, D-Ill., that will provide revenue for the tax breaks for members of the Armed Services and their families by sewing up a tax loop that allowed defense contractors, in particular, KBR (formerly a Halliburton subsidiary known as Kellogg, Brown & Root), to avoid paying their full share of payroll takes by creating shell companies in the Cayman Islands.

The practice allowed contractors to short-change their taxes by $100 million to Social Security and Medicare, according to Kerry's staff.

With the passage of the bill, Kerry said, "thousands of military families in Massachusetts will receive the benefits they deserve and big companies will pay their fair share of taxes rather than leaving hard working Americans with the bill."

Obama said that for "the sake of transparency and fairness in our tax system, we cannot allow federal contractors to set up shell corporations in tax shelters and shirk their responsibility to pay payroll taxes for their American employees."

First, it is substantially likely that a combination of Sen. Obama's secret service detail & the US State Dept & the respective commanding generals of US Forces in both Afghanistan & Iraq made those particular decisions.

Second, the Blackwater employees that Mr. Prince might assign to a presidential candidate / senator would very likely be of a different skill level than the folks assigned to a reporter or to a poobah with another sub-contracting firm.

And over 4  years old.

And no, there is no truth to the rumor (started by me) that not-quite-a-US-senator Lamont plans to join the Obama troupe during the vaction for some major campaign strategy sessions, hosted by various netrootz experts on national politics--all gratis, of course.