If anything were to go wrong during a flight, takeoff and landing are the two times that they want you to be able to react with zero hesitation. If something goes wrong and you have seconds to react, the less things you're fiddling with the more likely you are to survive.
It seems these reasons are made up by rational minds, trying to understand the ban. Like results from "Why the heck is this prohibited again?" pondering, but completely based on speculation.
So unless we can get some facts to back up these claims, I doubt that these replies help the OP. It sounds more like "Been there, thought about it, this is what I/my coworkers could come up with to explain this mistery"?
I think it is safe to say it's likely a combination of many things - this coupled with statistics (as mentioned before, very small % failure rate + very large flight volume = enough dead people to warrant having them turned off) seems the most plausible.
Not to mention that someone linked that it could very well be a problem with the cellular networks - if (hypothetically) you could bugger up an entire major tower with enough "hop" volume, I can see why the FAA or other organization would just want to have this as a cover-our-ass precaution, too.