Answers

Another question from the referrer-log: What's the constitutional problem if Tariana Turia will not vote (for the foreshore & seabed legislation)?

The answer is "Cabinet collective responsibility". We have a convention in this country that once a decision is made inside cabinet, they present a united front. This obviously rules out voting against legislation cabinet has approved, and even forbids criticising it publicly. Ministers who break this convention are almost always forced to resign.

This isn't a constitutional convention as such, but a matter of political pragmatism, in that it allows the Prime Minister to leverage the support of a small clique of supporters into a majority in the House. If the PM has a dedicated voting bloc (and she wouldn't be the PM if she didn't), then they can dominate Cabinet; collective responsibility turns Cabinet into a larger voting bloc which can dominate caucus; caucus (at least under FPP, where the system evolved) in turn dominates the House and allows the PM to push her program through. At the same time, collective responsability allows dissenting voices to be silenced, by bringing them inside the tent and then forcing them to shut up or mouth the party line.

This is a crock by any anarchist or democratic principles, and under MMP it has taken a bit of a beating. The requirements of coalition government have weakened the convention, and now there is an understanding that coalition partners sharing a Cabinet can "agree to disagree" and take different stances on a policy. This hasn't extended to members of the PM's party, however, and so Tariana Turia will be forced to toe the party line or be fired.

Update: Mike adds: "Labour has historically been far more intolerant of its MPs dissenting than National has. Labour MPs risk expulsion from the party if they cross the floor and I imagine they take a pretty dim view of abstentions... so the cabinet collective responsibility is probably only half the story."