Alexban, well you do have me intrigued, I have been in the checking training, management side of things for a lot longer than I care to remember, and up to now, emergency evacs have been considered as last choice due to the fact that somepeople usually get seriously injured in the event.
Possibly Boeing have decided that as the B737 is relatively close to the ground, (no offense ) to change there long standing reccomendations. For what its worth the latest ammendment for the 777 did not feature any chage in that area but when I get back from my current pairing I will try and track down a Boeing rep and see if he has an answer for you, usually a pretty slow process as they cover themselves in all sorts of protection before answering. Cheers.