How is Android being opensource as secure as Blackberry which is proprietory

I have worked on both Blackberry and Android mobile applications as developer They have production application builds as (several .cod files , .jad and .bat files) in case of Blackberry as final product and .apk in case of Android application .

In my effort to get code from Blackberry production apps was not possible

But

I have tried to do reverse engineering on Android .apk files using a tool found from internet and was quite successful in extracting .class files from builds .

Now my question is how can business applications be said to be secure on Android apps ?