Yes, Amazon is an Android app market.
And yes they simply accept the APK package.
It is essentially the same as Google Play except no upfront developer fee (Google Play charges $25). Same transaction split 70-30.
Just reread Markus's post.. looks like Amazon charges you $99 after the first year... So... I guess I'd have to see how my apps are doing and decide whether or not to pull them (hopefully the next one will be worth it).
I've had 1 download in the past 24 hours so... I imagine volume on Amazon is going to be much lower than Google Play.