You are correct 'crushthegmat', I haven't worked in the industry but made these statements based on bankers I have spoken to. I guess I was pretty vague though. I still stand by my statements, so I'll clarify (feel free to disagree):
By "interesting work", I didn't mean creating powerpoint slides and building models. I meant the actual deals that you work on. As an associate, I agree that you don't really get to be involved in much besides the details though.
By "work with smart people", I still stand by the fact that investment bankers are intelligent (you said genius, not me). For the most part, unintelligent people don't get into the top schools and get hired by the top banks. I'm sure there are exceptions. I also was referring to the customers that you work with (C-level employees, private equity folks, etc.).
I wasn't saying either of those two reasons is the main factor. Sure money is a primary factor, but I don't think most people go into IB post-MBA looking to make it into a long-term career. It's something they plan to do for 3-5 years, get the experience on their resume and exit into a more rewarding career that provides a better work-life balance. Therefore, I still say the exit options, in addition to the money, are the top reasons for going into IB post-MBA.