When I bought Civ V when it first came out, I had a DVD and it took hours to install the game on Steam - it seemed like the DVD was not even being used. So, what is the advantage of buying Gods & Kings from a store vs just downloading from Steam?
Quality is Job 1.01
If you have a DVD then you own it, you have the control on the data that are on it. But then you are also responsible for it. For instance you lose the DVD. Then it is your fault and you have to buy it again if you wanna have it again. And of course you have to run to the shop.
With Steam, you don't have to go to the shop, you just download it and pay and that's it. However I don't like it so much that I lose here control, in principle I don't have to care about a DVD, since I can redownload it. But what happens if Steam bankrupts, in case of doubt they would terminate the service. Probably, you could at least request a non-Steam patch, I would think.
Civ2 military advisor: "No complaints, Sir!"