Why do people spell Cummins with a "ings" ?

pitch wrote:
How well will my Cummings pull my trailer with my Alice Chambers tractor on it?

True story:

My wife worked for a farm-service government agency many years ago. The office hired a new secretary who grew up in farm country, but apparently none of it rubbed off. A couple weeks into the new secretary's job, she told my wife she had a call but she really couldn't understand what the call was about. She said she thought the caller's name was "Alice" Chalmers. :S