I am asking what is the specific criteria that makes stem cells survive the serum free medium (supplemented with B27, N2, FGF and EGF) and the non-stem cells die?
Stem cells do not proliferate and do not require the mitogenic factors present in serum. All other cells do proliferate and do require serum factors to stay alive and to proliferate (produce daughter cells).
Some will argue that the definition of stem cell is a 'cell that divides', but this is a recent (lay) corruption of the term. Stem cells, by definition, divide very rarely; they are quiescent!
Also, SC need different factors to support viability self-renewal that present in the supplement. Moreover some cytokines or growth factors in the culture medium could induce stem cell differentiation (opposite to what you want if your aim is maintain SC almost pure in culture)