I think in the future (maybe 5 years from now), writing programs for Android will become like making money with AdSense now: unless you are very large (like Facebook), or have a PR department (like NYTimes), expect letters like you now get from AdSense:
"It has come to our attention that <... blah blah ..>
As a result, we have disabled your application in Google Play store and removed it from devices where it has been installed"
And poof- all your work is gone!
Replace <...bah blah...> with "copyright", "inappropriate user generated content", "not fitting our 'business model'", "inducing users to install it", etc.
Amazon has effectively guaranteed it will stay that way for a while. Don't forget: Even early on, the Amazon Appstore was popular enough to force AT&T to stop blocking sideloading. It is only more popular today.