By an interesting side note, it has been reported that a jailbroken SurfaceRT revealed the full Windows 8 underneath--capable of running even legacy software, though admittedly not very well. The point is that Windows RT is to Windows as iOS is to OS X; they're intended to be part of an integrated package where data synchronization is nearly automatic while allowing the user to carry a much lighter and more convenient device for true mobility purposes.
A couple of obvious advantages to a tablet format vs the clamshell have to do with Apple's own PoS application and sales staff at places like car dealerships. When you're talking to customers who are wandering between products, you simply can't force them to sit down at a table to tell you what they want--they may not even know until they see it. With a tablet, the agent can walk with the customer/client and call up specific data on the spot and even start the purchase process (in the case of a car) before ever going back to a desk. In fact, Mercedes has made it possible to even go as far as signing the purchase contract on the tablet and having the printout ready in moments. This same capability is eminently possible with WinRT and since most car dealerships use Windows-based computers that means that the documents themselves are even more readily synchronized and logged.
In all honesty, your argument is little different than those decrying the original iPad when it was announced three years ago. The interesting thing is that even Apple was surprised at the uses--quality of life uses--that developed for it. Don't count Windows RT out as a mobility OS. I really believe you're going to be surprised at where Microsoft will go with their new system.
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