  The multiplicity of hadronic species created in elementary, and in
nucleus-nucleus collisions, are known to be well reproduced by the statistical
hadronization model, in its canonical and grand-canonical versions.To
understand the origin of the implied equilibrium we revisit the hadronization
models developed for e+e- annihilation to hadrons which imply spatial color
pre-confinement clusters forming at the end of the pQCD evolution, which decays
into on-shell hadrons/resonances. The classical ensemble description arises as
a consequence of decoherence and phase space dominance during cluster
formation, and decay.For A+A collisions we assume that hadronization occurs
from similar singlet clusters which will overlap spatially owing to the extreme
density. This is imaged in the transition to the grand-canonical ensemble.This
transition sets in with increasing A and collision centrality. It can be
described by a percolation model.
