That's what's known as a "tortured reading" of the statute.  There's nothing particularly special about King's Highways.  It just means a road: 
bigger than a cow path, 
for vehicular travel, 
that has been registered, 
that is controlled and maintained by the province.   

That's all in the definitions in Part I.  It's just a archaic legal formalism, probably dating back beyond Telford and McAdam, as is the approval of the Lt. Governor.  It is particularly telling that the other Acts, such as the HTA, use somewhat different phraseology.  If this were language with strong legislative intent, arguably you'd find greater consistency.  

The main thrust is that the roads themselves are no longer termed "King's Highways" at the MTO.  They are "provincial highways".  They are divided into 3 classes: "controlled-access", "secondary", and "tertiary".  This article needs to reflect current reality.