It makes sense that Surface owners would report greater satisfaction, since a larger portion of them use their device for its productivity features. A typical iPad owner, on the other hand, will be more interested in just using their device for media consumption. They might play some games on it, or check the news, or look at pictures of cats, but those are things they could be doing on their smartphone, which ultimately, an iPad is not much different from.
A Surface, on the other hand, does more things that a smartphone can't do well. It's more a laptop in a tablet format, whereas the iPad is more a smartphone in tablet form. Where one is a more portable version of a device with similar functionality, the other is bulkier than the device it functions most like. If someone's carrying around a smartphone, there simply isn't much need to bring an iPad with them as well.