If you had $600 burning a whole in your pocket (and you were having a baby), would you spend it on a diaper bag? Even if I never had to worry about money, I could not justify spending $600 on something to haul diapers, wipes, and a spare set of clothes. Even still, you can't deny that the people who will drop the equivalent of a car payment on a diaper bag or a mortgage payment on a stroller are a desirable target-market for baby product manufacturers.
It's like shooting fish in a barrel, really. These uber-consumers already think "expensive equals better," so all sellers have to do is jack up the prices and people open their wallets. Don't these people have anything better to do than to spend money of ridiculous baby gear they will likely use for less than a year? Luxury goods manufacturers have caught onto this trend, and diaper bags are one way they can tap into this market.
When I say expensive diaper bags, I'm not talking about a "pedestrian" $160 Petunia Picklebottom backpack. Oh, no. Even Kate Spade's nylon diaper bag (the parenting status symbol of the '90's) seems a little...played out at this point. Still, it's $215. I'm talking about Dooney & Bourke's Signature Diaper Bag ($325), which is fugly. Or Nest's platinum leather and metal-studded monstrosity ($285). For everyone who thinks it's reasonable to spend $350 on Coach's "Healthy Child" bag (matching wallet $188), I say: You're bored. Find a hobby.