Cap, if you are referring to the repeated advice to "stay where you are" if lost, that advice disappeared from the 2007 edition of the MBP (same text in 2008 edition but with colored pictures).
Consistent with its generally bad/disorganized writing, the current MBP is more ambiguous. It talks about how you might be able to "retrace your tracks" if lost and how you might determine your location (useless unless you are going to move). But it also advises you to "wait as calmly as you can for help to arrive."
Given several pages of criteria for an acceptable survival camp location, how do we know, in advance, that a "survival situation" will arises at a location within the range of the acceptable? ("Things rarely fail as planned.") What, for example, if you are on a steep scree slope in the blazing sun with no water when someone breaks an ankle. Just "wait" until rescue arrives? Maybe, but not likely.
What if someone gets severely injured or sick on Day 2 of a 14-day trek. Wait twelve+ days for the SAR effort to even start? How about some advice on planning self-rescue? How many stay? How many go? Who goes and who stays? That was once covered by B.S.A. literature.
The reality is we need to teach our youth that in the wilderness, as in life in general, there will be situations where they will have to use their best judgment. Move or stay? Buy or not? Join or avoid? Arbitrary rules give only the illusion of preparedness.