There’s no doubt that Android is on a real tear when it comes to smartphone sales, with an estimated 75% market share in the third quarter of this year. But what does this mean for the businesses of app developers and publishers?

Industry analyst Horace Dediu, of Asymco, has some worrying graphs on the subject. Specifically, he’s digging into an apparent reduction in Android users’ engagement with mobile shopping in the US – something that hints at wider issues for the platform.

His workings are worth reading in full, but the gist: “iPhone users are about three times more engaged in shopping with their devices than Android users. Two years ago the ratio was two to one,” he explains.

“The pattern is pretty clear with respect to Android: engagement is down as ownership is up. This pattern has not exhibited itself with iPhone, even though it has had a longer time in market… Why is Android attracting late adopters (or at least late adopter behavior) when the market is still emergent?”

Many developers still complain about Android, and a perceived unwillingness on the part of its users to pay for apps and content. Dediu’s research won’t set their minds at ease on this score.

It brings to mind a conversation I had with a few developers and publishers at the recent Guardian Mobile Business Summit though: the suspicion on their part that a lot of people – normal people, not geeks – are buying Android handsets because they want a nice touchscreen phone, but still mainly want to use it for voice calls and texting.

That said, I also wonder if this is something that will change over time: if people are only just getting their first smartphone – and this is a lot of people – it may take time for them to start using it for all the ‘smart’ uses developers and publishers are hoping for.