I would think they took into account cleaning (multiple times per day), maintenance, vandalism and loss of seating to come up with that number.

Especially the latter, since this isn't the first time they've done something insane for a few extra seats.

Putting the air intakes at the bottom of new trains (instead of on top as was the original manufacturers design) comes to mind, which lead to dozens of trains becoming unusable and needing weeks of repairs after a bit of snowfall...