Why should people be forced to marry in order to legalise what is a life long commitment to each other. In the case referred to by the OP, I read the couple didn't marry because he'd made a promise to his first wife, when she was dying, that he'd never re-marry. He and his 2nd life partner, the woman who took this case to the Courts, were together for 25 years before he died, they had 4 children together.
The law needs to change to catch up with the 21st century. Many couples prefer not to marry for various reasons, one of which may be they don't like the traditional view of a woman being given by one man, her father, to another, her husband. The legal situations in those relationships when a couple make what is a life long commitment to each other needs to be secured by changes in the law, that ensure so called 'common law wives' have the protection given in law to married women.