The air for the Air Conditoning/pressurization system does come from the pneumatics supplied by engines (and the APU of course). But these Ram Air Inlets are necessary to cool the bleed air in order for it to be used as conditioned air. The process of getting the air to the required temperature involes a process of taking hot air, then cooling it, heating it again, then cooling it again (to explain it in simple terms). This COLD (or better said cooler) ram air aids in doing that.
Hope this helps.