Keeping your money when you owe it for a service is, yes. It's called "theft of services".

EDIT: Perhaps I should put it more clearly...

If you sell goods on Google Play, I believe there is a fee of 30%. Now, imagine I found a bug in the Google Play store that meant that, even though I sold millions of copies of my app, I actually paid 0% to the Play Store. Do you think that Google would just accept that I'd found a bug in their software and therefore I owed them nothing? Do you think I owe them nothing?

Google chose to participate in a market where the costs were clearly labelled up-front and they didn't even have to pay a penny unless they made a significant profit!

Why the hell should they get away with paying nothing for a service that other people pay a lot of money for?