Perhaps your networks are a bit quicker at returning the updates to Microsoft than EE (for example!) here in the U.K.
The procedure, as I understand it, is that Microsoft first send any new firmware or OS updates directly to the network providers, so that they can add any 'bloatware etc.
The providers then return the updates to Microsoft who issue them to the end users on that particular network.
Hopefully I will receive something eventually, as I would rather wait to obtain an 'official' OTA update, rather than get one through the 'back door', as it were!