My understanding from chatting to a DC manufacturer is that, like Bob and KWS said, there are factors that differ between the modes. In some computers, the "Air" and "EANx" modes are actually different "programs" being run on the computer. When you switch between them, the saved "O2" data is lost, thus they try prevent you from doing so in case of high CNS exposure.
One of the reasons for this is/was battery life. DC manufacturers tend to do a LOT to reduce battery use, especially with non-chargeable, non-user replaceable batteries (most of the wrist computers for example)
With induction charging and user replaceable batteries ala Perdix and Teric, etc, many of these companies don't have the battery life concerns, so they are less likely to lock things out etc etc.
In many of these cases, the machines just run the nitrox mode regardless, the "Air" indication is just a preset to EANx21 and it won't show you the O2 clock unless it becomes an issue.
Maybe @Shearwater can give some insight into this.
