In-app purchases are a huge source of income for app developers, allowing them to remove some of the initial hesitance users might have in dropping a few bucks on an app, and instead letting them make their money bit-by-bit, as users pay a little here and there to unlock new features or add functionality. Today Amazon announced a new way for Kindle Fire users to make such purchases, with plans for the launch of its Amazon Coins virtual currency. The Coins will arrive this May, but we’re left asking ourselves, what’s the ...