That was frankly horribly researched. They started off with a supposition, and ignored any data that didn't help prove it.
They completely ignored that a new handset release tends to come in lockstep with a new OS release. This is relevant because it means many, many people are changing the operating characteristics of their existing handsets at the same time - leaving their phone not only not a "known constant", but potentially creating the same results even if a new generation of phone hadn't just appeared at the same time.
Seriously, if you take their graph and replace the labels for each 3g, 3gs, 4, 4s etc, with ios2, 3, 4, 5 .. the data is still accurate, but the take-away assumptions change entirely.
They ignored that geekbench scores show that scores for any given generation stay roughly constant over the phone's lifetime. That's a fantastic set of data that isn't coloured by changing expectations over time.
And they were quite happy to brush off that the samsung numbers showed exactly the same changes over time, as they didn't spike around releases. Completely ignoring that Android has entirely different update strategies (having to wait until your telco 'blesses' the update, etc).
If you look at their graphs, and think of each label as an OS release rather than coinciding with a new handset (which is still accurate), the story it now tells is that ios updates receive much larger adoption in hurry, when compared to adoption of android updates.
Which we already knew. Apple's update strategy is that every compatible handset is able to update "today", whereas android updates are staggered by various levels of support from different mffrs and different providers.