In any case, it seems unlikely that Mozilla would simply announce this without any consultation with their hardware partners. They're in a much better position to know what's possible than you or I!
> [W]e're jointly announcing that new devices from participating partners will receive the latest Android platform upgrades for 18 months after the device is first released, as long as the hardware allows ... and that's just the beginning. [1]
The announced partners were Verizon, HTC, Samsung, Sprint, Sony Ericsson, LG, T-Mobile, Vodafone, Motorola and AT&T. Since then, many have broken that promise[2]. Three of them (Sprint, T-Mobile, and LG) are now Firefox OS partners. I'm just skeptical that this time will be any different.
[1] http://googleblog.blogspot.com/2011/05/android-momentum-mobi...
[2] http://arstechnica.com/gadgets/2012/06/what-happened-to-the-...
As part of the licensing agreement to be called a "Firefox OS phone" I believe carriers must provide updates for a certain amount of time. For how long, I do not know. If the duration is public knowledge, I do not know. If partners will actually follow through, well... the articles you linked to paint a bleak picture. Of course, since our entire OS is open source, they can just use it on their own, and never release a single update, as long as they don't brand it a "Firefox OS phone."
I'm prototyping an add on right now that would detect a connected device, download updated pre-compiled images of the layers (gonk, gecko, gaia) and allow you to update them (if I verified that the update worked on your device beforehand, to make sure you wouldn't end up bricking your phone). Just trying to raise awareness within the org right now to get a green light to work on this more.
I can't see why Gecko/Gaia won't have the same problem, looking at the architecture docs.
My (fairly naive) understanding is that there is nothing comparable to the Gecko layer on Android (Dalvik seems in practice to be very intertwined with lower level code) so I'm not sure what conclusion you're drawing from the docs. Feel free to school me on it, though. :)
As for equivalence, gecko, among other things, has the drawing layer.
At least according to https://wiki.mozilla.org/B2G/Architecture, Gecko is using OpenGL ES 2.0 to do drawing.
This means it will be impacted by graphics driver bugs and issues, the same as Android is.
(Which is not surprising, since Gonk, the layer below it, started out as Android)
Look at it this way: anything that lives in Gonk will generally have exactly the same issues as Android does in terms of updates. There may be some pieces of it that are more generic than others (bluez, for example), but by and large, you will need to test on each phone model.
FWIW, the Gecko layer is essentially the same as Android's framework.
What functionality is provided by a high level layer differs a bit, but Android and Firefox OS are not as architecturally different as you seem to think.