Sure you can get. The free versions have adds and some of them missing a few options that the premium version's have. Im sure that there are app's that dont have a free version but the overall you will need have all a free version. There for i sayed every cause i don't found one single app i want/need that i couldn't have in case of it doesn't have a free version. The exception make the regulation.
I don't know about the 30% they have to give to google (poor of me to think they don't charge it) but as you sayed if you write a few real good apps you can have more out of your work at the most coders they work for a big companie.
lol yes i mean companies in german thats konzerne so i mixed something up in my head and used the english word concern in place of the german word konzerne ^^
Nice talk mate for the other part you posted