When you refresh products that make up 80% of your revenue, in one quarter, it costs money. When you're Apple, and expect to do $50bn of sales in the next quarter, that produces some pretty chunky payments. This chart shows Apple's capex and the increase in the money it has committed to in prepayments to suppliers (i.e. Foxcon and others). The sequencing of exactly when it pumps more money in is fascinating.
In the last 12 months, Apple spent $7.4bn on capex and committed to a further $7.6bn in additional prepayments, taking total prepayments on and off the balance sheet to no less than $26.3bn. Apple is locking in a massive amount of component and manufacturing capacity.