Who are the most profitable adopters of Wi-Fi technology?

Answer 1

Wi-Fi is not a 'stand-alone' business ..

I would say (almost without exception) no Vendor or Manufacturer is solely in the Wi-Fi Business .. (they make/sell PC's, Laptops, ADSL Modems, Mobile Phones etc etc that include Wi-Fi but are not only 'Wi-Fi' - even the main Wi-Fi chip manufactures (like Intel) also make other things ...))

You might as well ask "who are the most profitable adopters of the wheel ?"

If you mean which Industry ? then the answer is "the Computer Industry" (for wheels, it's the Car Industry).