You think 50 billion is a big number? It’s certainly a bit bigger than some other numbers that spring to mind, such as 48 billion, and that in itself gives Apple something to celebrate. As is customary with these App Store milestones, whichever lucky jackanape triggered their download at just the right millisecond will receive a gift — a $10,000 iTunes voucher, no less — while 50 runners-up will get $500-worth of credit each. But none of that is the really big, big news. What matters here is the rate of growth, which seems to have accelerated during the course of this year. It took 14 weeks for the App Store to get from 40 billion to 45 billion downloads between January and April, but less than 4 weeks to get from 45 to 50 billion. Now, we’re totally dependent on Apple’s internal stock-takers, not to mention an erratic ticker (“for illustrative purposes only”), but if those numbers are even remotely accurate then they represent something of a popularity surge.