Macrobrew can also get away with adjuncts - making their beer from corn, and cheaper - while a craft brew audience is going to be wary of corn beer (unless specifically marketed as such) and expect a more expensive malt bill.
I'd question the savings for a microbrewery on using adjuncts. Corn isn't easy to work with, especially on the standard microbrewery system with a combined mash/lauter tun without direct heating.
