I am from one of these regions but was not asked to provide FPP - I landed in 2012, applied for PR in 2010 under FWP, traveled to my home country for just 2 weeks since coming to Canada. There has to be some other criteria they are considering which we do not know the details of and hopefully will come to light soon. This cannot be purely random.
My only guess could be, under which FWP (the year) did you migrate to Canada - it could be that they had more stricter screening policy and the ones who came to canada with an older FWP are being asked to provide FP?
I came as an international student in 2009 and PR under PNP. We are 5 friends who have applied at the same time 3 are from east Europe and 2 are from the regions mentioned above. Only 2 from the regions above got FFP.