echokilo, yes, it is an oddity. Royalty has lots of oddities, like younger sons taking the throne ahead of older sisters. But generally King has only one meaning - he was the heir, now he's on the throne - whereas Queen has two meanings: she inherited the throne, or she married the man who did.
An exception: James II was chased away and William III, who was married to James's daugher Mary, was offered the throne. They agreed as long as they could rule jointly as William and Mary.