[pfdietz]

The advantage of combustion turbines is that there is much less transfer of heat across fluid/solid interfaces. In a simple cycle combustion turbine, no such transfer is needed. The heat is generated by combustion in the working fluid, which carries away the waste heat after expansion. Combined cycle does add a steam bottoming cycle that needs heat exchangers (before and after) and cooling towers, but most of the power is still coming from the combustion turbine, so the steam part is much smaller than in a pure steam plant of the same rated power.