It's not just about the cost of a pcb trace. A wider parallel bus means more potential skew which means either relaxing timing or tighter tolerances. The notion

It's not just about the cost of a pcb trace. A wider parallel bus means more potential skew which means either relaxing timing or tighter tolerances. The notional 12% cost for the extra ram bank and related hardware may not seem like much, but the margins on commodity computing equipment are razor thin. Consumers don't and won't buy on the basis of ECC being on a sticker on the box, so manufacturers correctly conclude that they should cut the feature or be undercut on price.