Games for Windows Live, a service that allows PC games to use the Microsoft Live network for multiplayer connectivity, is shutting down in July 2014 according to a since-deleted post on the Age of Empires Online support page.
Once the Games for Windows Live network shuts down, games that use the service such as Dark Souls and Resident Evil 5 will have their multiplayer features rendered inoperable. Those games will have to transfer to a new service such as Steamworks for multiplayer, which is expensive, time-consuming, and not guaranteed to happen. Developers will have to handle this change on a game-by-game basis, which will undoubtedly leave at least some games without multiplayer functionality.