I accept your point. But then a related question: why all this was not done with laptops e.g. tablet versions? Thinkpads have nice and light tablet versions which could serve pretty well for the task.
Because of the investment in testing and process by which devices are cleared by the FCC to be used for EFB.
http://www.faa.gov/other_visit/avia...afety/info/all_infos/media/2011/InFO11011.pdf
iPads are just one of the first tablets where the COTS device is both common enough to get certified and cheap enough that it's a no brainer to use.