A subset of features, certainly...
... but the fact that that subset is available when and where you need it without the added bulk and clumsiness of cabling and operation even as you travel on your own two feet give you capability no other form factor can provide. Yes, there have been full-OS powered tablets for a decade now, but their functionality was as severely limited by that OS as others say current tablets are limited by the lack of that full OS. The two OSes have been mutually incompatible up to now--we'll have to see how things progress in the future.
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