That's a terrible assumption. The problem with 'most' is it doesn't imply an exact number, it could be 0.01% more or 99.9% more and either is 'most'.
Nothing about that statement tells you it's near a 50:50 ratio.
Since we're not dealing with exact numbers (obviously 17 and 16 million units is rounded off) and because the difference is fairly small ~5%, it's less confusing to note a more specified relationship rather than an ambiguous and potentially confusing 'most'. Esp if later it's quoted out of context: "Most iOS device sales are not iPhones," (how many is most? how close is the margin?) is less informative than, "IDevices excluding the iPhone comprise about 5% more sales, with iPhones selling 16m units and other devices selling 17m."