I don't know about ceramic ovens, but for stones maybe the pores contain hot dry air that would cause a vapor pressure deficit that would draw water out of the dough. This air would not exist in a steel plate, though.
CDNpielover, I'm not talking about ceramic ovens, I'm talking about ceramic baking stones- pampered chef, old stone, williams sonoma, bed bath and beyond, along with almost every stone in commercial deck ovens. None of them are that absorptive/porous, so porosity is not a player. The only exception would be the incredibly cheap cast stones that you find at Walmart or the Fibrament stones. Those are porous- but it's their porosity that makes them incredibly weak- both thermally and physically. Where you have porosity, you have absorbed water. Water + heat = steam expansion = potential for cracking.