That's because Apple doesn't have support for flagging specific devices. You can't for example click check boxes that enable an app to be downloaded for iphone

That's because Apple doesn't have support for flagging specific devices. You can't for example click check boxes that enable an app to be downloaded for iphone 5 and iphone 4s but not iphone4. There are a variety of clever tricks you can use in some but not all cases. For example you can require a front facing camera to eliminate ipad1 but not ipad2. Unfortunately such tricks don't give devs complete coverage. It's a major issue that many devs struggle with. Apple is entirely at fault here for not supporting a very straight forward feature.