Sure, but don't try to hack this metric too much. Manufacturers use it and don't try to game it. They actually want to improve it. Apple partners with Foxcon to get this number at 5, and wouldn't have it at 5 if they didn't believe Foxcon could manage demand. Apple would maintain inventories in their warehouse if that was the case.
This metric speaks as much about Foxcon's success as it does Apple's.
Yes this is mostly down to Foxcon and that Apple sells a relatively small range of machines with little customization.
And it only counts for Apple's own stores, not machines on the shelf at Staples etc
And if you take this metric to extremes then something like the Morgan car company - where there is a multi-year waiting list for their hand built sportscars - is the most efficient company in the world !
This metric speaks as much about Foxcon's success as it does Apple's.