Can't we develop a master ROM?
Yes, this sounds like master key, that works for all locks. But, what I mean to say is, many OEMs, carriers, are, as you know, habituated to give delayed updates for Android. Many don't give them at all. There are many devices in the market which fit the minimum requirements criteria of latest versions but are still deprived of upgrades, mostly to suit the makers' business prospects. Now-a-days, there are several custom ROMs available from many developers who can provide upgraded software for respective phones. But why can't we have a software that fits all. Why do we need a different ROM for every device. As in, we have a single dvd of Windows or Ubuntu that can be installed on PCs of different configurations and made by different companies like Dell, Acer, or assembled. Just like that, can't we have an Android ROM that can be installed on all phones which like Windows or Ubuntu adapts to the configuration and hardware availability of the phone? Why do we have to go through this complex network of customizing ROMs for each device, do trial and error, etc.? This software can be made available to the public or at least developers when it has been tested at least on Google's Nexus devices. Many would argue that this might hit sales of OEMs, but when PCs were ruling, we still had this method in place and it didn't deter them.
(Correct me if this is already available or if there is a grave technical impossibility in doing this.)
Re: Can't we develop a master ROM?
One word - DRIVERS
What some (many?) don't realize is that those ROMs are customized to the device based on the HW (primarily the SoC) in the device, with the drivers baked in by the phone manufacturer. In order to deploy a "universal" ROM, you'd need to bake in the drivers for EVERY device. Phil mentioned on the podcast 2 weeks ago there are some 4200 devices supported by the AC app, imagine the size of that ROM. Doing this also requires that the SoC maker provide continued support for the chip.
It can be done with Windows because of the PnP nature of Windows, the drivers can be updated on the fly, and are installed over the internet (in many cases).
Think of an Android device like buying a Dell. You buy it from the store with a pre-set image, all the drivers are already there and the thing is ready to go. If you decide you don't want to use what Dell configures out of the box, you're on your own for installing the plain OS, including making sure you can get compatible device drivers.