Investment Banking has sky high salaries, not banking in general. That's mostly Mergers & Acquisitions, IPOs and Trading. The reason trading is so lucrative is obvious, if someone can make lots of money for you, they can do it for anybody so you haver tyo pay them lots to do it for you.
For M&A and IPOs it's also relatively simple; the differences in the amount of money you get can relatively easily be 20% or more depending on who's representing you. These are complicated transactions, you need a lot of expertise to do them, and you need a sales team in place to sell it, and an organisation capable of doing the research to drum up the deals. When you're dealing with huge amounts of money anyway and the top guys are vastly better than the mid market they'll be able to demand $BIGNUM because they're judges to be worth it.
For M&A and IPOs it's also relatively simple; the differences in the amount of money you get can relatively easily be 20% or more depending on who's representing you. These are complicated transactions, you need a lot of expertise to do them, and you need a sales team in place to sell it, and an organisation capable of doing the research to drum up the deals. When you're dealing with huge amounts of money anyway and the top guys are vastly better than the mid market they'll be able to demand $BIGNUM because they're judges to be worth it.