Having worked with the industry, you'd be surprised how much product gets returned. Some of it can be reconditioned. (AT&T Sells a lot of reconditioned on their site) and yes, shifted to other geographies, fire-sales etc. All i am saying is the value of a sale ( while technically a sale ) varies by manufacturer and model. Sales is a bell curve and timing means a lot.
Even the feds through Sarbanes-Oxely (the disaster that it is) requires that for public companies, all sales revenue meet certain criteria in order for the Mfr to claim it as 100% revenue.
So why don't they show the more interesting number, which is sell-through? Because its volatile as well and effected by timing, competitive announcements and would give them more visibility and less flexibility to reverse a negative trend. Also unless everyone reports sell-through you look worse than they do.