Name one good reason Nokia would have for withholding an update for a specific carrier variant model like the 810?
Casually walks in late provide clarification.
While you are correct that in most cases withholding a
tested, functioning update from consumers makes little sense for an OEM, and while it's true carriers will usually delay updates for devices with little sales or usage (usually due to the cost of testing the updates themselves.), this
may not be the case.
For instance, the rumored "LTE Update" that never came to be
*supposedly bricked or otherwise rendered the 810 useless, and as such was not officially announce or released to consumers. This may be the case again, where the black firmware (and to a further possible extent, Cyan) may of been found to be incompatible with the variant hardware of the 810, causing issues, instability, or even going as far as to render the device useless, and as such, the [black] firmware development for the 810 was ceased.
There is also the issue of the device being labeled as EOL. This means that
neither the OEM nor the carrier are obligated to provide support beyond that of warranty or future updates to the device. As such, Nokia (Now MS Mobile) may be refusing to allot time and resources into thorough development of the firmware for the 810 as so to better allot the very time and resources it would need to bigger, more important projects.
As such, even though the act of
carrier testing and pushing updates is up to the carrier,
development and initial testing are responsibility of the OEM, and as we do not know the development status of the variant firmware for the 810, it is
just as possible that Nokia themselves have halted development and release of Black for the Lumia 810 or any other firmware as much as it's possible that T-Mobile has chosen not to put forth the effort to release a finished firmware update due to the device's EOL status.
*I say this because in research of the rumored LTE update i once found an article, to which i forgot where (I think it was softpedia), quoting a response from a T-Mobile representative/correspondent stating that it did not pass testing stages due to issues with rendering the cellular antenna useless or otherwise bricking the device. However, as i can no longer find the article or confirm its source or reliability, i do not wish to state this as fact.
_____________________________________________________________________________
If you want your 810 updated, you'll either have to pay to get the developer preview or hope to get a free account.
Correction: In order to update using the Developer Preview (somewhat a misnomer), there are
two additional routes to joining the program.
•1: Retrieve either the Windows Phone SDK, which includes Visual Studio,
or the [custom] Windows Phone Lite SDK package, which includes only the registration and deployment tools, and then proceed to register your device. Registration is free and available to any user, but non-developers are limited to 1 device per account and only 2 apps (I believe it was) to be deployable per device (vs. 10 apps with a Developer account). Once registered, your device will be "developer" unlocked, and will allow registration with the Preview program.
•2: Register with AppStudio. Its free and once you've registered, you sign in with your MS account you signed up with in the Preview for Developers app and then you are on your way to 8.1