Over the past few years two more exceptions were added. When you are in trouble another minister gets assigned to take your questions. It could be the House Leader or it could be whoever is filling in for the PM. This is a great defensive tactic but it is just that, a defence mechanism that lets a minister off the hook. In the Chretien years, to use a Liberal example, when a minister was under attack, they took the heat themselves, day after day. Just think of Jane Stewart and what she went through for quite a few weeks.
If the situation got serious in QP, Chretien would rise and defend the minister. That was a big media story. Over the last couple of years that has changed: questions about ministerial expenses, as an example, have been answered by the House Leader. Why? If the minister spent the money, the minister should be able to tell voters why. A minister is supposed to be responsible for the department and it seems logical that this includes ministerial expenses incurred when performing departmental duties.