Where are you getting this information? I've never seen a bill for an app update (even a $0 bill) and I've not seen any mention of this anywhere else.
Actually, Apple did send out $0 receipts for updates in the early days. I have a few that list for-pay apps as 'Free' because they're updates. But I haven't received one of those in quite some time, so it looks like they've stopped doing it.
Whether they counted those 'sales' towards their billion is another matter.
"The pyramid is opening!" "Which one?" "The one with the ever-widening hole in it!" -- The Firesign Theatre