Example (BTC-E) :
1 month fee : 3.542 * 30 * 615 USD = 65349 USD
I see no mistake in the calculation; but that is the revenue, not profit. Considering that they have to pay salaries an other expenses, the profit from fees may be ratehr modest.
But they also make money from withdrawal fees; and the may be trading against their clients, with the advantage of knowing the orders of all traders before each trader knows those of other traders. (AFAIK this is illegal in stock exchanges, but there are no regulations for bitcoin exchanges, so why wouldn't they do it?)