Lowering MP In Camera Software

I have had multiple suppliers tell me for an outside parking lot type application to take a higher MP camera (i.e. 3MP) and "dumb it down to 2MP to enhance the WDR of the camera. My question is why not just purchase a 2MP camera or am I maybe not fully understanding what they are suggesting?

I've already been beaten to the punch by Ethan and Sean! I will add that 5MP cameras typically do not support true WDR (e.g., multiple exposure) while HD cameras frequently do. You'd be much better off getting a true 1080p/3MP WDR camera than a 5MP, regardless of what resolution you choose. Background - WDR tutorial http://ipvm.com/updates/1839