it's a bit more complicated than that, because anyone with the knowledge can create apps/programs for windows, mac, apple, iphones, etc etc. these are not open source.
open source means that the code itself has been made available to developers. you dont have to pay for it, you dont need to license your software then pay out royalties back to a parent company(google) like you would with other codes.
also there is MUCH less filtering of the apps. the general argument is this means less Quality Control in the app store, but if you look at our app store, where we have a choice in browsers, and the iphone store where they have blocked introduction of several browsers to date, the advantages of open source go a bit deeper than simple QC. howevre, this is one of the reasons why the ranking/comment system is SO important in our app store; a lot of that stuff really isnt even beta, its alpha, and we are the testers, so it's buyer beware.