At the risk of prolonging this totally unrelated (and somewhat pedantic) side debate, can you back that up with anything?
Like I said before; almost nothing is built using straight cement without aggregates, additives, or reinforcements - including pools. Maybe you're thinking of the grouting or plaster applied to the inside of a concrete pool form, but even that isn't just cement, it's a special mortar or 'plaster'. Concrete swimming pools are commonly built with steel reinforced concrete, either poured into forms, or sprayed into a negative form (shotcrete). Reinforced concrete can be polished to a mirror finish, so there is no concern with keeping it smooth.