Based on your logic, calculators shouldn't have ever been introduced in the classroom either because an abacus filled our needs. Or perhaps 128k of memory really was enough, since what possible use could we have for more memory or advanced technology if the status quo fills our current needs?
We are just beginning to untap the possibilities of mobile devices in the classroom, and to completely dismiss them as "nifty tech" is very short sighted. People tried to do the same ten years ago when laptops started appearing in classrooms. Had they succeeded, companies like Google would not even exist today.
We are seeing many interesting uses of mobile devices in education now that the devices are finally appearing in classrooms. However, until they become more ubiquitous and accepted, it will be impossible to fully demonstrate how much they can impact education.
Having spoken to professors who have personally experimented with iPads in classrooms, I can tell you it makes a day and night difference just in student engagement when they are given a textbook to study from versus being encouraged to explore a topic and discuss it using mobile devices like the iPad. I've observed biology classes where roughly half of the students used an iPad. These students consistently participated more than the other students. There are several reasons for this behavioral change, but I think the most important one is the design of the device and OS. It focuses on the single task at hand. When an app becomes the whole device and actually discourages multitasking, students pay attention more compared to their distracting laptop screens. Compared to laptop users, they also benefitted from a lack of a physical barrier from the laptop screen between the student and instructor. Those students that had no electronic device and just depended on the textbook generally participated the least and seemed least interested. It will be interesting to see how these devices continue to change how classrooms operate as more and more schools open up to the idea.
Keep in mind that the target audience is not tech savvy nerds, but the typical student, who for the most part is still afraid of using traditional laptops. These students, however, live off of their cell phones, so why not take advantage of an environment they are already comfortable in to encourage learning instead of forcing them into a foreign environment?