Hmm, you know, it's the Launch Escape System.

As we're at the very early stages of Project Constellation, it's now the time to think about escape means and possible failure events.
When NASA conceived the Shuttle, it didn't think about launch escape means after the first 4 flights.
Maybe what happened to Apollo 13 could increase the chances of a Lunar Orbit Rendez-Vous, rather than a Earth-Orbit Rendez-Vous and direct Moon landing.
Also, a Lunar Lander could be more basic than the famed LM (spacesuited astronauts standing outside, no pressurized cabin) and still be used as a escape pod if there's a problem on the way to the Moon (of course, that wouldn't be the case if the problem occured on the way back).

Raoul