You certainly can't blame anyone let alone Nacra or ISAF for broken masts. As Jeff said, any mast would break hitting the bottom.
Do you know how many Lasers break masts? Would you say that boat isn't sailable over 20?
How about 49ers? They break masts all the time and their masts are not cheap even despite the fact that they have multi-piece masts. The 49ers have also had multiple generations of masts and they still still break.
It's part of sailing a high performance boat.