Exploring how marginal chip value changes with stack size

[Galwegian]

I don't belive that ICM coincides with the brownian motion model although I have not checked this myself. ICM is a model based on the following assumptions (let t_i = number of chips that player i has and assume sum_i t_i = 1)

A) Prob(player i will win tourney) = t_i
B) Prob(player j will finish in (k+1)th position given that players i_1,...i_k have finished 1..k) = t_i/(1-t_i_1-...t_i_k)

Of course A is just a special case of B. However while there is a convincing argument that A is a good model of reality, I have not seen such an argument (myself) for B