To change the subject a bit:

Could/should software titles have thier ESRB rating be based not only on the game, but on any locked or hidden content?

At first, I would say "That is silly". However, what if that opens the door to scenarios such as this:

Rockstar makes a game, lets say "GTA: Greater Toronto Area".

The game is a standard GTA game, and would get an adults-only rating.

So, they modify all the mission script files and whatnot so that the game plays very G-rated. (Your missions are delivering pizza, driving Ms Daisy from point A to point B. No guns. Everybody jumps out of the way of your car, so nobody gets run over. No cars explode. No bad collisions. No blood, death or tittles.)

The game gets a lower rating, allowing kids to buy it.

A nameless "hacker" (actually a Rockstar employee) uploads a mod that alters all the mission scripts so that the game plays in it's natural, bloody fashion. They way Rockstar wanted the game to play.

The mod becomes well known and silently approved of. Everyone eventually ends up playing the modded version.

Rockstar gets a younger rating, which sells more copies and everybody is happy. They just got around the ESRB.

I don't mean to make negative implications against Rockstar in this example, I just used them for convenience.