Sales gimmick..military doesn't use match grade carriers and their weapons shoot fine. If you think having 'NM' laser engraved on the carrier will somehow make it more inherently accurate, I've got some parts to sell you myself.
As long as you are using a quality barrel and bolt (best purchased as a combo so headspace is verified) and your receiver isn't cut funny (some go through the extra trouble to lap the face of the receiver to ensure it is trued) you should have a straight shooting upper.
To get it shooting real consistant I would recommend you invest in a quality trigger––the ones that say 'match' on em ARE worth the money..see AR Gold, Giessele, etc.
With quality ammo, a good barrel, a good trigger, and solid shooting fundamentals, you will have an accurate system. Its not 1 thing that makes a rifle accurate, but all aspects working perfectly together to make it a precise and consistant shooting system.