Nibor - quite simpily, it's due to build quility - Bombardier seem to be more interested in getting a/c built and out of the workshop rather than sorting out all the defect's that are built in before shipping them to the customer - so hence when an airline get's them they take age's to find all the bug's in the system and rectify them. All Q400 operator's have found this to be the same.
But this problem does not just affect Bombadier - Embraer also have severe build quality problem's.
W.G