Tell any lay person on the street that MAME wasn't free software, and they'd ask you how much it cost. Tell them it wasn't open source, and they'd assume it meant the source wasn't available (if they even knew what source code was.)
But it just devolves into endless arguing over semantics. The ideology gets to be so strong that it's almost like religious dogma. And that's really not helping anyone.
Simply stating that MAME was non-commercial would be understood by everyone, and from there you'd be in a perfect position to then explain to people why you felt that all software should be allowed to be sold by anyone for profit. Distro CDs shipping with it, game museums having MAME cabinets set up, etc. Playing word semantics is just going to annoy people not already steeped in the FOSS world.
(for what it's worth, I also agreed to relicense my code that's inside MAME to GPLv2 for this new effort, so please don't consider me an enemy of GPL or anything.)