My understanding is they are the same bike but made from different material
not quite... the geometry is the same but the tubeset is different (cheaper and burlier) and the Bfe has a 44mm headtueb instead of tapered (used to be totally different back ends too but now more similar)
Do Souls tie themselves in knots over rough ground or are prone to breaking
and that's why Cotic introduced the BFe
Different frames for different things, Bfe is certified for 160mm forks, doesn't mean you have to run them, or that they ride best with them but you can if you want, Soul is 140mm max.
I would imagine **most** people who bought a Bfe did so because it was a fair bit cheaper than the Soul, and for those that bought because they want the extra strength, I doubt they would have ever actually take a Soul to breaking point anyway. There are of course exceptions but the Soul is a very tough frame, where as the Bfe is a very VERY tough frame.
where as the soul is xc
Not really, it seems to have this mis-conception, its a proper tough old trail frame, it's just that it happens to be OK as an XC bike as well
Edit - See Cy's rant about that exact point! (02/09/2013: Soul - Tough as Old Boots)