As far as I remember, 10 years was the default setting when creating a keystore in Eclipse. I think, about 5 years ago, Android development got kind of mainstream so I expect a lot of apps to be un-updatable in the Play Store in 5 years.
So far, I haven't found a solution on how to "prolong" a certificate's lifetime. Is there one? Will Google implement a way to set up your app with a new certificate? Of course, my scenario doesn't affect TOO many apps but I think there will be a considerable amount of SO questions on just that in 3-5 years.
Any ideas?