[jseliger]

The other interesting thing is that, as far as I know, until the late 90s the entire installed base of computers was bought practically every year. There'd be 10M computers one year and 10M bought the next. In that kind of fluid market a company can take over without winning converts (Joel Spolsky wrote about it here: http://www.joelonsoftware.com/articles/APIWar.html).

Today, PC sales are steady or falling because everyone in the developed world has one already. Someone buying a second or third computer is getting a tablet.