Seems like we get a site like this every few days. Are they making crazy money or is there some other reason everyones is making one? Are they just really easy to make? Maybe because payment process disruption has occurred? What's up?
Underwriting merchants and get verified by Visa/MasterCard as a payment service provider is a bitch. Aggregating credit cards is a heavily regulated area - but most of these sites are unaware of this issue.
We initially started on Stripe, and got told what we were doing was unregulated/not allowed on stripe, so we then grabbed a coffee with them and learnt about this process.
In fact I was grabbing coffee with Sahil (Gumroad) a few months ago and they've just run into this issue themselves - which they are starting to solve. so you'll probably notice them asking you for more information to underwrite you, unless they find a way around this.
That's also why we ask users to go through an activate process.
Then all the billing/charging services came along. Recurly, Chargify, Spreedly, CheddarGetter, etc. These made billing and charging your own customers easier. They never really handled "products" but I think they paved the way a bit by showing that having easy APIs is important.
Now you have services like Stripe. So, you can do recurring billing and individual charges. You can let your customers setup their own accounts (via Stripe Connect) but still keep the business logic in your app. This also takes care of the disbursements/payout issue and puts the onus of chargebacks on the user. The API is easy. PCI compliance is not as much of a problem. Transaction fees are in line with PayPal (but our BrainTree fees are lower). You can build a tool like this, a marketplace like Etsy, a crowdfunding site, etc. ... If you look through Stripe posts on HN, the biggest gripe is always international payments. I built www.bngal.com because it was easy and fun.
It will be interesting to see what's next ... possibly integration with in-person payment systems (like Square) or maybe cardless payments (linked to bank account?).
I started working on Chec in late 2010/early 2011, before groad launched. (https://www.facebook.com/checkoutbyswipe, if you wanna trace down to the day that page was setup) - It's a long story between then and today.
Short Version - University in England -> AngelPad Incubator -> Raised large seed -> Founder Split -> Had to rebuild new company.