Apple had sold its
billionth iOS device last November. If we split the sales in that quarter (74.5 iPhones + 21.4 iPads/2 = 47.95) and add the last quarter sales of 61.2 iPhones + 12.6 iPads, plus a quarter of that (the June quarter will be less than the March quarter) for the last four weeks (18.45), add an estimate of 4 million iPod touch sold since then, we get an estimate of 1.144 billion iOS devices sold by now.
The only iOS devices not being able to run iOS 7 or 8 are the original iPhone, the 3G, the 3GS, the original iPad and the first four generations of iPod touch. Now, if we add up all iPhone sales until the end of Q2 2010 (when the iPhone 4 was launched), all iPad sales until the end of Q1 2011 (when the iPad 2 was launched), and all iPod touch sales since the end of Q3 2011 (when the 5th gen iPod touch was launched) we get a total of about
145 million iOS devices that cannot run iOS 7 or 8. This is about 13% of the total (and we know that those devices were still sold beyond the dates their successors were launched, ie, that is underestimating their numbers but since the sales starts never aligned perfectly with the quarterly published sales figures, there is some approximation in this anyway).
Does this chart then mean that at least two thirds of those iOS devices are no longer in use?