Nah. It's just hard to find out about it.
How, exactly, do Apple or Samsung, never mind Google, find out when one of these devices goes to the landfill. Who tells them, and with what reliability? Why should anyone do so?
I think the answer is that there are a lot more dead devices out there (phones in particular) than are being acknowledged, but I'll be darned if anyone has a good handle on it, so we shouldn't be surprised that it isn't talked about.
I suspect Google's Play Store and Apple's various iCloud services have a pretty reasonable measure of the active number of units.
As a thought exercise we can try this:
Last July they had sold 365m iOS devices, 140m iMessage users.
Since then 600m iOS devices sold, so the expectation is that at least 235m active users. Yesterday they also claimed 300m iCloud users, so now the lower bound is 300m active devices. There are similar numbers floating about GameCenter usage, too.
Now this isn't a great lower bound because you can totally use an iPhone without GameCenter, or iMessage (and, in fact, you can have users use one and not the other, or neither). The other problem is that you can have multiple devices using one GameCenter/iCloud/iMessage account. I have 6 devices in my household tied to one GameCenter and three iMessage accounts, and I'm certain other multiple device households have the same 'issue'.
Essentially what it boils down to is that a person may have an iPhone and an iPad, and pair the two, such that they count as one user with two devices. The extent of this is hard to evaluate but a naive increase by 100m based on the number of iPads sold gives you 400m as the baseline of units in service.
In any case, add to that also the number of units from 2011 and 2010 still in operation that aren't new sales (the delta between June 2013 and July 2012), and you have probably a reasonable number between 70% to 80% of the 600m.
The same logic likely also holds for Google Play devices, number of activations per year, and the assumption that the normal folk don't replace a perfectly good phone every 2 years (so 2010 until 2013) means a good 80% or even 90% of Android's devices sold is still active, or about 800m or so.