The simple truth is that people like the interviewee in the article just don't work on nearly as hard of problems as do Google engineers. Being an engineer myself, I've never had a finance job, but I've had plenty of friends and roommates who have. They need to know some math and have some Excel skills, but most of their time is spent on phone calls and Powerpoint decks. That's why even an easy first question in an interview for an engineering position (e.g. write a C function that reverses a string) is more difficult than the questions asked of these guys. Just look at the example of the most grueling question in the article. Describe the process of a leveraged buyout? That doesn't really require any analytical skills, creativity, or problem solving.
I really think it's suboptimal to have finance people running our businesses, Wall St., and our economy. In my experience, they have a hugely inflated sense of self-worth, which is based mostly on their hugely inflated salaries.
Out of interest, how do you know this for a fact? I presume you were actually at most of these interviews?
I know for a fact that most public accounts of Google interviews are wrong. I have no reason to believe that public accounts of financial company interviews are right. I just assume that everything I read on the Internet is wrong until proven right. ;-)
FWIW, my Google interview was much harder than my two interviews with financial software startups. But I'm not certain if those startups are representative of the financial industry as a whole. Things might be different at Goldman, or hedge funds, or PE.