People are talking about this like it's a nationwide salary cap. It's only for companies seeking taxpayer-funded bailouts. Basically, if they are so incompetent in their business dealings that they require a bailout, then it's a good bet that nobody there should be making more than $500,000 a year anyway.
If a company doesn't want to submit to the salary cap, then just don't ask for a bailout, it's that easy.
I actually agree with Obama on this.