I happen to know a little about the history of pinball machines (a friend of mine is one of the bigger pinball collectors in Italy). In the fifties, pinball machines had scores that advanced by one when you hit some target. In the sixties, they advanced by ten. In the seventies, by one hundred. The latest ones, by thousands. I call this the "score inflation". It's psychologically pleasing for the player to score "1 billion, 234 millions and 9 thousands" points instead of "12.349" points. But if you look at the pinball machine code (or mechanical relays, depending on the year) you will see that the two scores need the same effort to be reached.
Now, it seems a little silly, but I believe that later on we will see version numbers increase by ten, then by a hundred, and so on.
Now we have Firefox 6. In 6 months we will have firefox 12, then Opera could switch from 12 to 22 to play "catch up" with Firefox, and IE from 9 to 19... then Firefox will release version 23, and Opera version 40 (to make it even, they will jump over version 32), and eventually Firefox vill release version 100, and so on.
I suppose I will see somebrowers release "345K" (as in 345.000) before I die.