Chris Ziegler of The Verge was finally able to clarify (via a source, presumably within Google) what Google means exactly when they give Android activation numbers. Essentially, it’s when you activate Google services on the device.
In other words, Kindle Fire, Nook, etc, don’t count as Android devices by this metric. Seems a bit odd, no? Android is an open ecosystem, but Google only counts you if use their services.
Sure, you can argue that Google has no way of knowing the numbers for those other Android devices, but they could at least acknowledge them. It’s weird that they don’t given the millions of units this would add overall ecosystem bottom line.