[Q] Why can't I buy (or download) a stock copy of android to install on any device? - Galaxy S II Q&A, Help & Troubleshooting

This is sort of a technical question regarding the architecture of the Android OS and possibly its licensing, etc... For most Windows computers, you can simply download, or buy a copy of Windows directly from Microsoft, install it on any x86 hardware and it will be fully optimized (speed, battery life, etc...). Why can't Google make a build of Android like this so I can simply buy a copy from them and install it on my phone with OEM hardware overtop of their bloated and skinned version of Android? For example, why can I not buy, say a Galaxy SII, and then buy a copy of 'Vanilla Android' from Google and install it legitimately and have it work? I realize that I can flash a copy of CM7 or some other custom ROM from open source developers but I would like to be able to just simply buy a copy of stock android, directly from Google, install it on my device, and have it work, just like with a Windows computer. Is the reason Google does not do this due to licensing issues? Or is there some other reason for this seemingly obvious solution to all the annoying OEM and Carrier bloatware that most Android phones are subject to?
Note: I realize this question has already been asked but I was hoping for a reason for why Google can't (or won't) provide an alternate build of android that works on all devices in addition to the stock builds that come with phones. As well, why do device manufacturers insist on being total d'bags and not just simply release all the drivers for their phones so we can choose the best phone for the reasons you want to (i.e. speed, build quality, price, specs etc...) and not because of the stupid bloatware or lack thereof?!?

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Because, stock Android means absolutely NO drivers installed for a specific device so your phone WILL NOT function (No Touchscreen, No signal, etc). Samsung releases their own firmware after compiling their own Baseband, Kernel and ROM. This contains their touchscreen drivers, wireless drivers, etc. When you change the ROM, you essentially void the warranty, so manufacturers do not encourage it, but they do allow you to combine their components together for you to make your own custom ROM (using their baseband, kernel and/or Samsung official rom as their base roms)
They build their own ROMs so that they know what they are managing, and what they need to fix and update. Also there's also a USP for every product released, let's say, Sony Ericsson's UI with Timescape, Samsung's Touch-Wiz UI, Motorola's Blur, etc. If you want a stock phone then I suggest you go for the Galaxy Nexus, or one of those Nexus phones that Google themselves maintain.
If you want a stock copy of Android OS on the Galaxy S II, try CyanogenMod, it is a custom ROM which is very stock and runs on every device, BUT each device, you need to download a DIFFERENT rom, because their different drivers. If you expect Google to release drivers for each phone for their stock OS'es, they will go insane as their are an uncountable amount of Android devices released on a weekly basis

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Great answer Nicholas I read this about an hour ago & spent 10 minutes trying to come up with a detailed answer that would make sense to a user of any experience level. Then I gave up

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I'm referring to all smartphones not only SGS2 here.
Ad part 1 - It could be difficult. Every device is different and going this way Google would have to prepare/upgrade it's OS for every device on the market. This is hell of a job, so it's up to device manufacturer or community to do this. I think smartphones differ to much (much more than PCs), so it's not possible to create one system for all. Besides, warranty issues - manufacturer of the device could not be responsible for problems caused by someone else's OS (this is understandable). It's also worth to notice that flashing a smartphone is a process completly different than installing OS on PC as PC cannot be bricked in this process. Give users easy way to flash anything on their phones and you have another gate to problems as they will surely flash everything including windows dlls on their phones. You say that on PC any OS can be installed, I say FOR NOW. In a few years You will have a choice - cheaper PC, windows only, OS only from manufacturer or more expensive one and you install anything You want. Why do you think UEFI was created? It will happen unless PC market collapses, because according to some market analytics we are entering post-PC era and mobile devices will became our main devices.
Ad part 2 - It's just business model. Manufacturer/carrier does not sell You the device (that's how they see it), they sell You some bunch of features and have no interest in You adding more of them to Your device. SGS2 is a flagship phone and it's kernel sources are released. It has unlocked bootloader also. You payed accordingly - so you free to do much more things, and use full hardware potential. With lower-end devices - manufacturers prefer that You buy another device instead of upgrading current one. Market insist on lower prices, but with every device unlocked/released drivers etc. prices would be much higher and smartphones much less affordable. Devices like SGS2 are created for very specific users - power users/devs/businessmans/enthusiasts.
I think that You want impossible. IMHO it's almost miracle that Samsung released some smartphones with unlocked bootloader so You can flash everything You want. (btw. it was the reason for me to choose sgs2). And about that "bloatware obsession" - I just don't understand why some people are sooo obsessive. I don't find some app usefull - I don't use it, period. But TBH I must say that Samsung put some serious s**t preinstalled on SGS2. Sometimes it outranks even worst market junk.