They support Windows, iPhone, and Android. I've developed for all 3... not that I did much besides fix bugs on the XBox app for a month before my contract ended (I admittedly was there for years prior on a different team).
Let's consider what they'd actually be doing. On Windows... they're already full blown computers. We probably aren't playing with BT devices.
Android API's don't actually work the way they're said to. My friend implemented BlueTooth on Android, and told me the woes of getting every phone to behave the same. Imagine doing that in AGK.
iOS: This is actually really consistent. Probably the only one to be supported if they do.
Long story short, Android is a pile of sand, windows doesn't do mobile much, and apple... is extremely easy even if you do it native. Seriously it's like 5 callbacks with 2 NSDictionaries since the hardware part is taken care of.
If you're going straight into hardware, then why would you keep it in a hobbyist game developer's toy? (I'm assuming that's the target market, not trying to knock anything, after all I bought 2 copies, one me, one for my friend during the sale.)