Pirate software is software distributed other than in accordance with the licence - e.g. because I've made a copy without the copyright holder's permission. The GPL obligates distributors who don't modify the software in at least two distinct ways:
Best Buy clearly don't attempt to prevent you copying a SuSE box set you bought from them, so the second isn't relevant to them. As for the first part, one would assume that Best Buy have arrangement in place with their suppliers to ensure that they're indemnified against breach - either by having their suppliers provide source as part of the package, or by having their suppliers provide and honour the written offer.
This isn't much different to other products with some degree of legal risk, such as washing machines; Best Buy will take on some of the risk themselves, but will push as much as they can back to their suppliers.
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