The big boss might have two. Everyone is who is anyone has his own. You are clearly a junior manager if you share a secretary. Only the peons type.
This changed. It changed slowly. For years, senior people did not type their own email, or even read it on a screen. A secretary would print it out, and the exec would dictate, live or to a recorded, any responses. Did the exec know how to type? No. Why should he? Having a keyboard is a sign that you don't have any power.
Long nails indicate that you don't do manual work. High heels mean you don't walk long distances. An expensive watch means you can afford one -- it tells the time about as accurately and about as reliably as a mid-priced or cheap watch.
How does it change? Very simply: when the people who are high-status do a certain thing, people who want to be like them copy it. When technical entrepreneurs became rich, people copied them. Do successful Wall Streeters carry Blackberries? Everybody else did, too.
Status, yes. And sexism, too: typing is women's work. Low status.