For every 100 web pageviews on an iPad, a Kindle gets 5, a Galaxy gets 3, and a Surface gets 0.22
I’m waiting for someone to do a comprehensive study on this with the ability to control for hardware, software, connection, and websites. I do get the feeling that iPads are better optimized for surfing but I also know that there are other considerations that influence behavior such as screen size and battery life. There’s also things a user cannot directly control such as auto-refresh of browsers when switching tabs.
My hypothesis is that iPads are more enjoyable to use and so they get more use and while that may be the majority of the explanation, there are other factors at play.