Some interesting thoughts....

Personally, I highly doubt that a Duty Free store in a major airport is going to refuse to stock a product line for fear of hurting revenue at a bar or restaurant that is under different ownership. Maybe in a smaller airport, but not anywhere with a significant amount of traffic.

Regarding cost, at least in Scandinavia, alcohol duty is very high away from the airport, so the duty free stores are relatively great value. The 500ml Nogne O beers that I bought recently were roughly 50 NOK each (~£5 or $6.50), which is approximately half of what they would cost in an Oslo city bar.