Apple has launched a new 10 Billion App Countdown promotion to celebrate the downloading of the ten billionth app from the App Store. “As of today, nearly 10 billion apps have been downloaded from the App Store worldwide,” reads the promotion’s web page. “Which is almost as amazing as the apps themselves. So we want to say thanks. Download the 10 billionth app, and you could win a US $10,000 iTunes Gift Card. Just visit the…