Besides server outage, I wonder about app use while abroad or in areas with patchy or no mobile coverage.
Here in Ireland, providers charge 5 to 10 Euro per MB while roaming depending in the country the user is roaming in. Now imagine if the user switches between various games each evening, all which need to do DRM authentication for each launch. The user could end up running up a nasty data usage bill even if they never browse the web or used any other data usage while abroad.
Another problem, which I'm sure is not limited to Ireland is patchy / no coverage areas, especially if there is not a Wi-Fi alternative.