Rick, have you found a solution to this? In my case, granted on the beta version of iOS, I noticed that code will only react the second time the same VC was initialized which is strange, too.

There's no rule to that and no other store-fronts, really, but developers who (also) sell off the Mac App Store usually use services of either FastSpring or Paddle, as John said above, to run their stores. We've been using FastSpring since 2009 (so before the Mac App Store even opened). It does require work on your end to set these stores up, both in the applications (license checking for example) and on web site. If you also sell on the Mac App Store, this means you have to build two separate versions. It's doable and not hard on Xcode but again, additional work. There are benefits to selling outside the Mac App Store (you have emails of your customers, lower commissions, can participate in sales outside the app store, can let people try your app or have a different trial mechanism, can sell apps that are not allowed on the Mac App Store and have a backup solution in case Apple decides not allow your app in the store for any reason). There are also some web site that list apps that are not on the Mac App Store, like macupdate.com (probably the largest of them), so that's an additional way to get discovered.