Creating a false sense of urgency is a cornerstone of modern marketing. The only difference between this and any other marketing campaign is that you just happened to catch them this time. This is just like when you go to an electronics store and they put the super expensive tv (almost) nobody buys right next to the still very expensive but comparably more modest model. You are more likely to buy that second tv even…
I don't think it is a good example. It is often a real technical limitation - they aren't able to keep consistent inventory count between branches, warehouses and internet sites. Other reason for "few available" is some form of dropshipping - they don't really have any items.