Paul Birch, my co-founder had been investing in some pretty well-known companies for a few years, and wanted to get back to the craft. I've been doing lots hacks, and wanted to do something around taking rapid experiments and turning them into businesses (if they worked). Nick Marsh, the other co-founder is from a design background, and was similar inspired about building a studio that builds digital products. He talks about the Eames Studio of the 21st century.
We looked at a number of hacks for our first product, and picked Bitsy because we thought it would be quick to hack (we were wrong!), had a good prospect of being revenue positive early, gave a leg up to the little guy (our core proposition as a company), and it was about enabling people that we know to sell digital products online easily.
I have a bunch of friends who could or should be selling online but don't know where to start. Being unable to price for the UK market, having to set up a paypal account, the legal issues involved, are all barriers for those people, and we wanted to make a very easy way for them to do that. With some elegance (Jon Gold is on the team), focusing on selling socially (via Twitter, Facebook and so on), and in a way that supplements the marketplaces. If you've done the hard work selling something, why give away a large percentage other than for payment processing?
From a US point of view, it probably looks like a solved problem, but in the UK it's really not. So that's where the initial motivation came from - help our friends, and people like them, make income from the digital things they make.