Here's something depressing and slightly horrifying: roughly 1.2 million people are using Android 1.5—a three year old operating system that looks like a Chinese bootleg of itself. How? Why? It gets worse.
In addition to the 1,000,000+ souls using Android "Cupcake" 1.5—which at its debut had just introduced state of the art features like auto screen rotation and YouTube uploads—a staggering quarter of all Android devices are using the 2.2 release. That version, Froyo, is two years old itself, and over 75 million people are using it. It's not as jarringly antiquated as 1.5, but 75 million is a big number for software that came out years ago.
What accounts for this? Sloth? Ignorance? Blame it on Google? Probably some nice cocktail of all three. These figures presumably include handsets used in "developing" (poor) markets, where we should be surprised and pleased people have access to smartphones at all. But there's undoubtedly a factor of Google and phone makers having botched the way they do business. Some older phones just aren't powerful enough to run the newer versions of Android, but in those tens and tens and tens of millions, there are certainly many that are.
Either Google's abandoned them, some hardware company abandoned them, or the confluence of the two made it too confusing to upgrade out of software dating back to when Boom Boom Pow was still on the radio.
Apple often finds ways to gut-punch owners of its older phones (an iPhone 3G slowed to molasses via software, Siri banned from the iPhone 4 without reason), but the fact remains that an iPhone 3GS owner—a phone that came out in 2009—can upgrade to 2012's latest without any trouble at all. It's safe to assume none of these many millions will be eating Ice Cream Sandwich.
Figures via Google