It's obvious the Lumia 920 is a device that is not cares about. They only care about the new models and the 520 because it sold so much. They don't care that the 920 gets a worse camera with every firmware update. And I think denim won't do anything for our beloved 920.
OK Dan the Downer.
my 920's camera has performed well enough as a matter of fact. for the sake of my enlightenment could you inform me how the camera has degraded please? (I'm serious, I know they tweak camera stuff, but never really seen it get worse in my eyes, etc.)
think of it this way:
You are Microsoft. Your goal is to make money. (that's how they all are internally, so don't think its "evil M$ hurr hurr")
the 920 is out of production, its no longer being sold.
it is coming on three years old as a model.
it has seen three, four updates with firmwares to boot to date. Not counting Preview builds.
Windows Phone 8.1 Update is a minor update which still plays perfectly well with Lumia Cyan.
it is still going to be updated officially to your latest OS approaching on the horizon: Windows 10.
Your device lineup is increasingly getting larger. (cutting a firmware upgrade for something as minor as the 8.1 Update is perfectly reasonable IMHO.)
No, you don't go 110% effort on an aging device until the last unit dies. You don't make new hardware features tailored to every device in your portfolio. You try to balance all sorts of things. Customers like you with their expectations and/or entitlement. The finite resources you have to put into various things. You have limited manpower, limited funds, limited time. Could time spent on an older device be better used elsewhere? Shareholders. etc.
Not saying to dump a device as soon as it isn't being sold, because that doesn't end up well in the end. *cough* cheapo Androids *cough*
It's just you cant go forever. The 920 has had its upgrades and its time in the limelight. Now its fading into the background as a new generation steps up. It's still around, still used, but not top-of-the-list priority.