There's always been a lot of rumors about the random statistics on artifact armor. For example, some people believed that because the Rogue's Bonnet does INT+5 and "Steal +1" that SE was hinting that INT affects steal rates.
You'll have to decide for yourself, but here's what makes sense to me. The ability score modifications are placed in a sensible fashion. I.E, body pieces give VIT; head, MND and INT; feet, give AGI; hands, DEX; legs, AGI. Look at the Rogue Set (http://wiki.ffxiclopedia.org/wiki/Rogue%27s_Attire_Set) again, and look at the pattern. Look at the Wizard's Attire (http://wiki.ffxiclopedia.org/wiki/Wizard%27s_Attire_Set). Granted, the stats don't fit a perfect mold. I.E, the Warlock's Tabard does CHR+5 which doesn't fully make sense. Or the Chaos Burgeonet does STR+4 which, again, doesn't follow this mold. But, typically, they do. The stats are not tell tale signs of anything, they're just extra.