As with everything on the web, our fate is in the hands of the mighty browser vendors. In this case, all the major browsers (IE, Safari, Firefox and Chrome) agree that my 64-bit Windows machine is a Win32 platform. This means they’re sticking to the old definition as far as Windows goes, because none of them are compiled for 64-bit thus far. Look on the bright side though: at least they all agree on something for once.
It seems like we’re a bit luckier when it comes to handheld and media devices. As you’ve already stated in your question, the iPhone, iPod and iPad each got a unique value, even though they’re all running the same operating system. All of Nintendo’s and Sony’s devices are returning unique values too. So only now navigator.platform is starting to look interesting.
But then Opera Mini for iPhone comes along, messing things up again. Opera Mini actually returns a code engine version number, which is a completely different interpretation of platform than anything we’ve come across so far. So now we’re back where we started and we start to understand why there’s so little information on this subject out there.
Even though the interpretations vary and I don’t have a complete answer for you, I did feel like I should add my 2 cents for anyone else out there researching the navigator.platform property.
Below is a (definitely non-definite) list of the values I know of that I could verify with multiple sources. Because of the vague definition, I’m not too sure what the best way to order these is. For now I divided them into a few categories based on operating system or device brand and listed additional information and release dates where applicable.
It’s really hard to test for Android devices. Android devices will return Android just as often as some version of Linux. For example on a Nexus 5 phone, both the Android browser and Chrome return Linux armv7l. In rare cases Android devices can even return null (instead of undefined).