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Android (s goog) has raced ahead of iOS (s aapl) in smartphone share but it continues to fall behind in usage and engagement in the U.S. The latest data from IBM (s ibm) on Black Friday shopping traffic underscores just how much iOS outperforms Android. Asymco has some good charts that highlight the engagement gap.

IBM said that 77 percent of mobile traffic on Black Friday came from iOS devices. This despite the fact that Comscore said that Android has 52.5 percent of smartphone subscribers while iOS has 34.3 percent. Some of it comes down to the iPad, which is still the dominant tablet and produces the most traffic compared to iPhones and Android phones. But like the iPhone, the iPad exhibits outsized usage patterns beyond its actual marketshare. Gartner said in the third quarter, iPad shipments have dropped to 50.4 percent. But IBM said it contributed 88 percent of the tablet traffic over the long weekend.

This is a pattern than has been in place over the last few years. But now that Android is now the top dog on smartphones marketshare-wise and is eating into the iPad’s lead thanks to the Kindle Fire (s amzn), Nook (s bks) and other Android tablets, why is iOS still so dominant?

Here are some theories we’ve gathered from around the web alongside our thoughts:

Horace Dediu of Asymco wondered if Android was attracting more late adopters, who were prone to do less with their phones than hardcore smartphone users. But he’s not convinced that’s the answer. Perhaps, it has more to do with “design considerations” or “user experience flaws or integration.”

One thought is that Android users are more apt to want things for free, so they’re not as likely to shop for things on their devices. We’ve seen a gap in how Android and iOS users are willing to pay for apps — Android users prefer free apps — but that difference is going down over time.

Some Android users are just graduating up from a feature phone and really don’t understand all they can do with their device. Considering the declining number of feature phone options, it’s possible that people are graduating to cheap Android devices, but just still talk and text on them, something Daring Fireball’s John Gruber mentioned before.

Tim Windsor from Digitally Speaking goes a step further, saying that most iOS buyers are specifically buying their devices for the features they can access, while most Android users are just buying what’s available to them. Most, he believes, aren’t interested in serious computing power.

Jason Grisby of Cloud Four recently wrote that the gap doesn’t exist when looking at web traffic over cellular. It’s only when you examine iOS and Android traffic over Wi-Fi that a usage gap emerges. He believes that Android users might not be aware of the availability of Wi-Fi networks through their device or are in lower income brackets and have less access to Wi-Fi networks.

Some people believe there is no gap at the high end when looking top Android devices. The problem is with cheaper and older Android devices, which don’t provide as good an experience or are saddled with older versions of Android, which are worse at browsing. It is true there are more cheap Android phones options available, so that might contribute to some of the gap. And a majority of Android users are still on devices running Android 2. 0 x.

x. Apple users are more likely to use apps, which can provide a better user experience. Android users who turn to a browser may not find it as inviting or engaging.

It’s also possible that shopping data is not an accurate proxy for engagement. NetMarketShare earlier this year said, however, also came up with general browsing data that showed iOS devices have 65 percent of mobile traffic compared to 20 percent for Android.

To be clear, the data we’re looking at is from the U.S. only, and it’s based primarily on shopping traffic. My theory is that there are people who walk into a cellular store, see only a handful of feature phones available and a salesperson who is heavily pushing Android devices. If they want to walk out with a new phone, it’s likely going to be an Android unless they came in already looking for an iPhone. Those people may not be savvy now, but they will get more experienced over time. What are your theories on this Android paradox?