I've heard that this rust issue is resolved mainly because mazda is now sourcing their sheet metal from another location.
apparently, the previous sources had contaminated metal, but this is supposed to have been adressed since 2007-2008.
as for surface contamination (tiny rust spots) they are due to the type of paint finish, and avoidable/removable by good maintenance/wash/claybar/wax. I used to have a 2008.5 cristal white pearl mazdaspeed 3 for the last 5 years and had no rust issues except from the surface rust (cwp is more prone to this).
Future will tell how the CX5 will age and hopefully not rust... I am very confident that it will not considering my last 5 years of mazdaspeed ownership was rust free.