You can't just apply the margin like that. You have to estimate the marginal cost of the extra business.
For something like banking I'm fairly certain that the marginal cost is tiny. It takes a lot of money to setup all the systems needed for moving money around, but once they are in place the difference between 10b and 11b flowing through them is tiny. As such HSBC probably pocketed most of that revenue.
2) Your point about expected value is well taken, but here you are saying something far different from what themagician said and I was objecting to.