The superfluous 's'

Why do people add an 's' to the end of words that aren't supposed to have an 's' at the end? It bugs me no end.

The biggest department store in Australia is called Myer, but most people I know call it 'Myers'. The main road that goes along the top of Flagstaff Hill in Adelaide (heading East-West) is called Black Road, but most people I know call it 'Blacks Road'. Why? This abomination probably occurs all the time in all English-speaking cultures, but the Scots take it to another level.

In Clydebank, where I was born, there used to be a sewing machine factory belonging to Singer Manufacturing Company. Logically, this should be abbreviated to just Singer. For example: "Your mum's a minger, she works at Singer." But no. Neither was the name adulterated by the simple addition of an 's'. Ask anyone who lived in Clydebank prior to 1980 and they'll tell you they knew someone who worked at 'Singerses'.

So when Scotland takes over Australia we will all be shopping at Myerses and driving down Blackses Road, just you wait and see.