IOS does not suffer from many problems of fragmentation, that we know it, but it is normal that there are people who still use devices a little old for life time imposed by those of Cupertino, and just users who already have an Apple with IOS 3.1.3 device can not download apps from the App Store.
Apparently this “bug” is existing since the last update which took place the day 16 of this month, has even opened a thread on the official forums of Apple, but no official response on this issue. According to reports from users, even you can install applications and update them but only if the IOS device is connected via iTunes.
The strange thing of all this is that Apple still has not acted officially, so I still dare to call this incident as a “failure”, but it is likely that in Cupertino want to unsubscribe to their older devices. Most likely Apple to rule soon on this incident and we provide official information on this subject.
Update: Well, the important thing is since last night the AppStore has been updated again (and in silence by Apple), and it works (you can see it in the last posts of thread created within the community of Apple that you send). But the “UPDATE” button still does not work on the updates of the AppStore tab, so updates must be made one by one, seeking and re-buying each application that has an update ne devices with iOS3.1.x