PS. Developers want to eat, support their families, pay their mortgages, etc. so patience is not an option here.
If this is their main concern, then why are they spending their time on such a low payout time consuming endeavor? "Not enough people are buying my iPhone app fast enough for long enough" isn't something a mortgage lender or a hungry kid wants to hear.
So yea, I didn't mean for it to sound quite so dramatic, like the app store doesn't have any tail at all, because that's not really true. But for getting a read on your product's success and earning some useful revenue for the next project, those first 2 months in my experience are key.
That is probably a conservative estimate on the AppStore (and people ask me why I won't develop for it).
By way of comparison, roughly .3% of my sales to date were within 6 weeks of release. If you consider the release of my web version to also count, then about that bumps up to about 5%.
Old PS2 games still sell, 10 years after the platform was introduced. A good, simple game for the iPhone platform may still be sellable, in some format, in 2019. And the installed base of compatible devices could be 20x larger.
PS. There was an invention hundreds of years ago that addresses exactly the need for paying current costs while waiting for long-term profitable projects to pan out. It's called 'finance'. Considering only 2-month windows of costs and revenues as if we were talking about subsistence farmers is a rookie myopia.