There many hosting provider, datacenter, payment gatway to choose from. But just 2 appstore to use (technically android can have as many as you want, but how many pp use 3rd store right now?)
The problem I have with third party app stores is you have to open up permissions to install any third-party app -- you can't just say "Trust apps from the following app stores" (at least that I've found, although it has been a while since the last time I looked into it).
compare to china where google is blocked, which as a result has dozens of competing appstores. each phone brand has their own, and then some.
i do believe that if google didn't have an appstore that it forces android licensees to use, then we would have a similar variety of appstores world wide.
