It's only exactly what they'd do anyway if the chosen location was getting their new HQ anyway. While I don't necessarily agree with it on a personal level, this is a pretty basic "supply vs demand" situation.
Companies do sometimes indulge in incentives brinkmanship by threatening to move if they don't get the right offer. But, assuming this isn't Amazon just playing that game with Seattle, they do have pretty open options. Like it or not, companies do go after tax incentives and local job creation is pretty important to politicians. And it's not clear it shouldn't be given that's pretty central to the economic health of a city or area.
It's also worth noting that Amazon isn't just a tech company; they're a huge retailer. Walmart has no particular problem having their headquarters in Bentonville Arkansas.
NW Arkansas airport also has a surprising amount of service for an airport in that location - American, Delta, and United regional affiliates. serve most of their hubs from there. Presumably a lot of this traffic is either Walmart corporate or suppliers that have located an office in Northwest Arkansas to be close to Walmart. I'm not saying that Amazon would pick a place like that - Walmart has always been in Arkansas. But air service will come if necessary.
That makes me wonder about Pittsburgh and Raleigh-Durham, which both have underused airports (PIT as a former US Airways hub, RDU a former American hub).
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