Except the hardware vendors provide the drivers needed to run Windows on their hardware as a separate download from the OS. While the hardware may work with the Windows Update version of the drivers, often times you can get more advanced features if you go to the vendor's site and grab the driver package.
Android is similar except the OS is delivered to the device with the drivers pre-packaged because the OEM is providing the OS fully tested (though things DO slip through). Windows Phone works the same way as Android. iOS is similar but it's less transparent, all the time spent installing the OTA updates isn't JUST updating the OS files but also determining which Apple device it's on and optimizing the software for that hardware as well as disabling features of the OS that aren't compatible with that hardware (Siri on iPad2 comes to mind).
BTW, I use all of Google's services, Google Play Services is using 58 MB of the RAM on my Moto X. While it has the highest RAM usage of anything running on my phone (not by much) it's hardly a "resource hog".