I was curious about that too. At the end of the day, I don't know if it matters. Gretchen and Elliot were Walt's chip on his shoulder - his driving reason to blame everything but himself.
By the way, one scene I love in retrospect is the flashback to Walt and Gretchen in a classroom talking about the elements that compose a human body. Hydrogen, Carbon, etc. But it didn't add up to 100%. Did it imply that they were forgetting the human soul? The conscience?