Cisco, Juniper (and many others) are doing the same thing: Release new hardware revisions that are incompatible with older software versions.
There are two distinct cases:
- new device model which requires some OS features (device drivers or some such) which were not available in older OS releases.
- factory default OS release installation
It is clear for case #1 that it would be highway to bricked device if one tried to install OS release without required features. And information about factory installed release is there to make sure this doesn't happen ... So if a device is clearly marked as "v7 only", then purchaser is kind of warned about consequences. But when buying device which is on the market a while one doesn't expect to be forced to use shiny new ROS version (which he wasn't prepared for yet).
The case #2, which is shortcut to burn this information into device, proves troublesome though. If a device is HW wise identical to devices of same model produced some time ago, it would very probably run same old ROS release as the older device just fine. So basically what would be extremely nice would be burning same lowest release version information in all devices of same HW revision, regardless factory default software. But that would probably require some additional steps in production line and MT decided not to do it this way.
When ROS is more or less stable, this doesn't matter as much ... there's no big difference between e.g. 6.46.2 and 6.48.4 ... if there's some minor problem, one can go to 6.49.5 and ROS will still behave more or less the same. The difference between v6 and v7 is large and it'll take some more time before v7 stabilizes enough for set-and-forget installations.