A WSJ article citing how lower inventory balances allows Apple to invest more than rival Samsung in R&D:
Meanwhile, back in China, armies of low-cost labor in Zhengzhou, also known as “iPhone City,” and other manufacturing hubs help Apple churn out the devices so quickly that it only needs about a week of global inventory. That makes more cash available for R&D. Rival Samsung, which does more of its own manufacturing, has held about 60 days of inventory on average in the past five years.