您注意三星Galaxy S4与MetroPCS Z500不同。
You notice Samsung Galaxy S4 is different than MetroPCS Z500.
Does the manufactuer update the drivers depending on the hardware their Android OS is tweaked. For, I.e., different support drivers. This question doesn't concern policy, but the software Android runs on different running platforms with different hardware.
For example extra hardware must be mapped diferently to access, so new Linix drivers must be written right?
Short answer: yes.
In fact, it's a little more complicated than that. The device manufacturer or OEM buys different components (chips and sensors) from other manufacturers. Some of those components (such as the SoC or chipset) in turn contain hardware designed by other companies. For example, an LG phone might contain a SoC manufactured by Qualcomm, which in turn contains a GPU designed by ARM.
Just like how the hardware contains components from different vendors, so does the software. In the example, when ARM licenses (sells) the GPU design to Qualcomm, they also supply the source code for a reference driver for the GPU design. (They'd include source for whatever platforms Qualcomm is interested in, including Android.) Qualcomm would adjust all the parameters of the driver (such as the memory map, which you mentioned) for their SoC, and put it together with drivers for all the other components of the SoC.
Then, when LG buys the SoC from Qualcomm, Qualcomm would supply this combined driver to LG. LG puts this together with the drivers for other parts of the phone (such as the touch screen), adds their UI customizations, and builds a ROM image that they can flash onto the phone during manufacture.
There's sometimes an extra step, too: the carrier might change the ROM to include more pre-installed apps, a different boot animation, or other customizations.
So, although in general each component manufacturer or designer is responsible for the driver for their own components, that driver is changed further down the line.
That's what usually delays an Android update being rolled out to the end user's device: Even if the AOSP (Android Open Source Project) announced a new Android version being available two months ago, it's still only available to Nexus users (their drivers etc. are included with AOSP) -- while OEMs first need to adjust their drivers, and test how that goes along with the new Android version. For some devices, they might even decide it's not worth it, and not adjusting the new version.
The same applies once more to vendors/carriers shipping branded devices: they first need to wait for the manufacturers to finish their adjustments, and only then can start adjusting the branding (and testing their adjustments again). Another delay. But now you might uderstand why some carriers proudly announce a 4.0.x update to some devices, while 4.2 is long available and even 4.3 already knocking at the door.