Had to share that one with you...
Apple bets people will come and find them, and go on a waiting list if necessary, thus they can afford to no bother pre-marketing in the open to partners. The other tech companies hedge their bets and make sure their boxes are on as many pallets in as many partner's warehouses as possible.
The film industry also does something like this when marketing films to toy manufacturers and marketing partners for tie-ins, but it does not generally market major films to distributors and theaters, they accept them sight-unseen (which is, come to think of it, exactly the sort of condition Apple compels on its partners). The exception to this rule are art-house and independent films that are sold to theater circuits and distributors at trade shows, also known as "film festivals" and "film markets."