In SUSY we add a second higgs doublet, so we end up with eight degrees of freedom. Three are eaten by the Standard model gauge bosons, leaving 5 higgs bosons.
my questions is: why are the 3 degrees of freedom eaten only by Standard model particles rather than 3 Standard model and 3 SUSY particles: why the asymmetry? Would the situation be different without SUSY-breaking? If it helps to visualize the problem, the asymmetry is most striking if you imagine that we lived in a world where the mass scales where reversed: the SM is off at some high SUSY-breaking scale, and our world consists of superparters. Would we not have gauge theory and electroweak symmetry breaking, or would the gaugino sector require electroweak symmetry breaking?
In the most well-known case (GMSB) m0 and m1/2 are generated by gravitational interactions which is flavor independent. Higgsino is a superpartner of Higgs scalar which has a mass m1/2, which is again scale dependent due to renormalization effects. Your counting for number of physical Higgs scalar fields as 8-3=5 is absolutely correct as m1/2 is the source of Higgsino mass which is unrelated to spontaneous breaking of SU(2)L x U(1)Y gauge symmetry.
PS: Interestingly, off diagonal terms in the 4x4 neutralino (gaugino-Higgsino) mass matrix is related to VEVs of neutral Higgs scalars. That is those are tied to the EW symmetry breaking scale.
The reason is that there aren't any such (massless) gauge bosons, that can accommodate the scalars as longitudinal polarization modes in theories, where supersymmetry is a global symmetry: the matter fields are in multiplets with spins 1/2 and 0 (the spin 1/2 are the usual matter fields and the spin 0 are the superpartners) and the gauge fields are in multiplets with spins 1 and 1/2 (the spin 1 are the usual gauge fields and the spin 1/2 are the superpartners). But the gauge fields of the latter multiplets are the gauge fields of the Standard Model-or of its extensions, that would involve a larger gauge group. Such, additional, gauge bosons arise, either in extensions of the Standard Model, to larger gauge groups-or in supergravity-which is how the goldstino is avoided: supersymmetry, in the latter case, is a gauge symmetry and the gravitino becomes massive through the Brout-Englert-Higgs mechanism, that eliminates the goldstino.
I think that the most simple way of looking this is looking at the number of spin states. For a particle with a spin greater than zero, you have two spin states in the massless case (not depending on the spin) and 2s+1 spin states in the massive case. Since all MSSM (without supergravity) superpartners have at most spin 1/2, they cannot absorb any Goldstones, since they already have the correct amount of degrees of freedom.
As was already mentioned, the gravitino, which is a spin 3/2 particle, can absorb the two spin states coming from the goldstino, which emerges, when supersymmetry is spontaneously broken.
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