Would one be able to achieve a similar effect by simply opening the windows on a regular basis? (Assuming all the other principles around good air-flow and ventilation were following in the building layout.)
Yes, but modern humidity controls are able to regulate moisture levels while also reclaiming heat. That is, if you open all the windows your warm/cool air will flow out while fresh air flows in; an energy recovery ventilator will partially precondition the fresh air as it flows into the house, using the outgoing air as the source.
