It is one thing for a sysadmin to take care of a small problem remotely using his iPad/Android/Surface. But I seriously doubt they are using that as their only or main device for carrying out their duties. Sure, there are some workers that could carry out their jobs with only a tablet. But there are just as many, if not more, who can not.
As for the Chromebook, I would rather have a fully functional 13" inch laptop or 10" netbook than a portable thin client.
I am sure there are plenty of people out there who don't need anything more capable than these devices, but that is not generally true in the business world.
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