Dealbook points out that novels about Wall Street seem to be obsessed with the brand names that their characters consume and, especially, wear. "A pair of Ferragamo loafers, in particular, seems to be the Chekhov's gun of financial thrillers -- wear those in Chapter 1, and you're doing 20 to life by the epilogue."
This is only one of the reasons that novels about Wall Street are terrible (as Epicurean Dealmaker, from whom I got the link, says, "it looks like Wall Street is still waiting for its Dickens. Or even its Grisham.") But it's a particularly strange one. I've worked at Wall Street firms (not, except for one stint as a Merrill Lynch Summer Associate, in finance, however). I can't say that the denizens of the trading floor and the investment banking groups seemed to be noticeably well, or even noticeably expensively dressed. To be sure, they were clearly not shopping the seconds rack at Men's Wearhouse. But these were not, in general, men who took pride in matching a lovingly-chosen pair of shoes with their bespoke suits. They mostly looked like any other sunlight-and-exercise-deprived guy who can afford to walk into Brooks Brothers and buy a suit.