They just need an Order in Council under CERA to cancel the census, right?

It was a bit more than that - a Proclamation by GG.
Proclamation - Revocation of the 2011 Census

Sampling, and Census less frequently would be the best of both worlds :)

I think that this thread is derailed enough, so back on topic.

Has Hone Harawira been derailed himself by the several issues he didn't consider (Māori Party sees agreement not binding to Mana Party & by-election, financial and party registration issues etc.) and quietly shelved his notice to resign Te Tai Tokerau? The time to have resigned was when he said he would, not after discovering he is forced to Act just to hold on to his credibility and his 'Mana'.

I don't know what the law said in 1931 or 1941, but the Statistics Act 1975 is in absolutist terms. The Government *must* hold a census, or amend the law.

Exactly; the government must abide by the 1975 act, and as it states,

The census of population and dwellings of New Zealand shall be taken by the Department in the year 1976 and in every fifth year thereafter.

That would suggest that 2012 - 2015 are ruled out. The govt has already stated that amending legislation is needed to allow for the non-census of 2011 - they have not said that the census would be transferred to another year. As to the absolutist terms of the 1975 Act, it is quite likely that will be the part of the Act amended - a simple addition something like "unless the Statistician considers that the census could not be successfully completed in any census year". It saves having to repeat the process in any future circumstance, and it avoids prescribing further changes - if the census were to be postponed until (say) 2014 what happens to the subsequent 2016, 2021, 2026 etc. census in relation to the phrase "in every fifth year thereafter"? They are just as fixed in the Act as was the 2011 census.

Reliance on Census data by both business and public sectors is far more pervasive now than 70 and 80 years ago. And 5 years is a relatively longer wait now than then, given the pace of life.

Conversely, the amount of planning required from stats nz is that much more than it was way back whenever. And if you'd lived through way back then as well as the here and now then the present lustrum would seem so much shorter ... but that is as irrelevant as your 'pace of life' analysis - in any case, most countries hold their censes once every ten years, Australia and Japan every 5 years while next week's German census is the first since 1987.
Census data during the Depression and the War would have been tainted by the unnatural displacement of substantial sections of the population - just as is the case now vis-a-vis the displaced population of Christchurch post 22 Feb. It is reasonable to assume that no census worth its salt can be taken while there are still large numbers or persons unnaturally displaced, unemployed, homeless or living without sanitation, and given that it will take a considerable time to alleviate this situation AND the time it will take to plan another census we'd not be that far short of March 2016 anyway.

Only if the census never happens. I don't imagine that will be the case.

It has happened twice before (1931 & 1941), why is the 2011 census any different?
The circumstances aren't important: Depression; War; Earthquake, what is notable is that in both previous cases the 5 year cycle wasn't broken by the skipping of a census.