Goal-moving aside, I think it makes sense for the company going forward.
It's probably better to sell 20 million units with 20 million people locked into the MS ecosystem, than to sell 40 million units with only 10 million locked in the ecosystem. MS is slowly moving towards a service-oriented subscription business (Office 365, Onedrive, Skype). MS will also be expanding LIVE to a variety of Windows devices over time (phones, tablets, PCs, TV boxes). If people start using Xbox Live as their main "digital account" for games, movies, apps, etc, then they're much more likely to stick with MS over the competition.
Sony has an ecosystem of their own, but it's much more limited than what Microsoft is doing.