Sadly it's pretty easy to get fake or stolen credit card numbers. Even barring that, it's pretty easy to phish normal users (who all have credit cards on their accounts, as a sibling post points out) and use them to vote without their knowledge.

As far as "this is crap, go build something better" - that's tough to say when developers show high (albeit juked via cross-promotion) download numbers, and is also difficult for developers to stomach without some kind of objective measure of what makes for a good app.