There are plenty of reasons, but here is an excellent graphic representation of why Obama is trying to cap salaries for executives.
And if that fails to convince you, then think of this fact. Bank of America has received over $40 Billion in TARP (Bailout) money. They're currently worth $25 Billion. We could have bought every single share of their stock and saved $15 Billion dollars. Instead, we own about 7% of the bank.
Yay for treasury secretaries who used to be CEO of Goldman Sachs!