First off, the amount of cash a company has isn't indicative of its success. The goal of these companies is to deliver return to shareholders. Holding cash doesn't do that unless it's used for something.
And secondly, where are people getting this $70 billion number? I've seen it in tons of posts and I can't, for the life of me, find where. I'm looking at their 10Q right now...
Where are you getting $76 billion from? That issue notwithstanding, you're right about the lack of leaks. They don't want users holding off purchasing because of what's coming next. The only thing they can do to that effect is not release any details at all that a new iPhone is coming, even if most people know it is.