It is becoming increasingly frequent for publishers to release new games without a "true" standalone retail release; in other words, the disc you're buying is little more than a Battle.net/Steam key, likely with an installer provided so you don't have to spend time downloading it from their digital distribution service (I believe some games include a disc that doesn't serve much of a purpose at all, providing a tiny downloader app for the game you could easily download yourself -- the real product you're buying lies in the key). However, the game is still tied to Battle.net/Steam; really, all you've done by going out and purchasing the retail copy is saved yourself some bandwidth and, depending on your connection speed and closest game retail outlet, time.
This practice is now occuring on all Blizzard/Battle.net games, if I am not mistaken, and it is very common for Steam games, whether or not they use SteamWorks. A few games on gog.com also follow this release practice. Even games which used to have a standalone retail release that did not have to be tied to a distribution service are now being repackaged to follow this practice.
I personally used to enjoy having a retail copy because it both allows you to have a way to install your game without an Internet connection, and it usually looks nice on a shelf. However, unfortunately it seems like it's not worth it to buy these newer retail "releases" since they are just a repackaged version of the digital distribution; even instruction manuals are released digitally now, usually exclusively. My personal opinions aside, I just wanted to make the point that physical and digital releases are the same for most games nowadays.