Today we learned that Microsoft has bought roughly an 18% stake in Barnes & Noble’s eBook department. The news may have shocked many folks, but I saw it coming. How? Simple: content is important and despite the popularity of devices, people really buy into ecosystems because of content.

Strong ecosystems are not that hard to find: Amazon offers eBooks, Music, Movies. Apple also provides eBooks, Music, Movies and they throw in Apps. The more content a person purchases, the more difficult it is to leave a particular ecosystem. People will leave (or consider leaving) a platform if you offer something really compelling.

Microsoft’s strength is in gaming and xbox fans won’t mind accessing their gaming content via tablet. However, that massive non-gamer market will avoid the “gamer tablet” much like they avoid non-casual consoles. Buying into Barnes & Noble’s eBook department adds an important type of content to Microsoft’s nacent mobile platform. Perhaps they’ll acquire Hulu?