[IANPG]
If we take the odds of a startup surviving as 1:100, then the odds of both Digg and Reddit surviving are 1:10.000. If we assume that either Reddit will crush Digg or vice versa, the odds of Digg crushing Reddit are 1:20.000. If we assume that the odds that the marketplace will support more than one company are 10:1 the odds that Digg will crush Reddit go to 1:200.000.
Even if the denominator us high by an order of magnitude, the first order problem is just surviving and that depends on luck and execution. All the other factors do as well.
The mistake is in confusing game theory with a Sport metaphor. Sport focuses attention on beating particular opponents. Game theory prioritizes a diversity of outcomes. Beating Digg isn't an objective measure of success. Reddit could beat Digg and not create value.
My apologies for just being a random person on the internet and being neither PG nor Alexis Ohanian.