Ha, I think James has completely missed the point. It isn't a keyboard that makes tablets productive, it is Windows desktop + Office. This is what iPad and Android users have been screaming for, for a long time. Granted there has been a big push by "office style" app developers to fill the hole but really nothing is as good as MS Office.
On the whole tablets have gotten more popular and people have tried to fit them into their needs even if not ideal for that. Students get a TF Prime with keyboard doc Docs to Go or Quick Office or whatever and then try and make that work for school use. The keyboard segment has always been a big part of tablets but until the Surface they were bulky and used bluetooth requiring separate batteries and pairing or an awkward micro usb cable for some devices and cases. Just general popularity of tablets and people trying to figure out how to make them laptop replacements accounts for seeing more being used with keyboards.
To me what he really seems to be saying is that the Surface raised his awareness of keyboards on tablets so he started noticing them in public more. Sort of like when you buy a new car and then you start seeing them on the road everywhere because your awareness has been increased. I think that his opening line is still very applicable "That writing has often generated a reaction that this is not really a solution for productive use. That was largely due to the tablets, either iPads or Android tablets." That is still the case, it is due to iPads and Androids lacking the equivalent of Windows desktop and Office, not keyboards.