The Half-life of Dominance

This idea is doing the rounds - that as computers/internet become more integrated in our lives, and therefore the number of players increases due to growing revenue, the dominant player will not last as long until they are usurped:

IBM 1950-1980
Microsoft 1984-1998
Google 2001-

If each period is only half as long as the previous, then Google only has two years left to reign. Feels right to me - it can't take much longer for a worthy challenger to appear...