Comparing apples and oranges, or Apples and Androids in this case.
The difference is shareware doesn't have a big MarketPlace icon right there on your desktop to search and download the software.
You're being led to the MarketPlace as a trusted location with no caveats whatsoever with Google both charging developers to join, connecting cell carrier billing, and promoting the Apps.
Since Apple does due diligence on their AppStore the Android users expect the same and should get nothing less.
Even Firefox checks out the add-ons before they can be be downloaded from the Firefox site so it's not a big deal, just needs to be done.
Huge difference between vetting for malicious content or bad software vs picking and choosing based pure bias.