He may argue he is making the same decision Key did last year, but there are differences. The TPP was a hot political issue this time last year and there were to be demonstrations against it at Waitangi. Naturally a prime minister would want to address the subject at that time.
The temperature is much lower this year. More important, the country has a new prime minister and the public does not yet have a reading on his commitment to everything Waitangi represents. Government insiders and iwi leaders may know his commitment to Treaty principles is second to none in the National Party, but he is Prime Minister now. That means the public looks to him to see where the Government is going, and his appearances matter.
He could have quietly agreed to the marae's request. A powhiri is a welcoming ceremony and an occasion for speeches of greeting and good will. There is plenty a prime minister can usefully say in the spirit of the powhiri - about Waitangi and the nation it founded - without descending to the usual arguments of politics.
To get to the powhiri, prime ministers and their attendants usually have to walk through a protest on the road outside the marae. Key was jostled as he walked to the gate with Sir Pita Sharples the first time he went there as Prime Minister but he declared it would not deter him from returning. The incidents outside the gate are all the public can see and remember of Waitangi Day each year, though they happen the day before.
Every prime minister faces the challenge of finding a way to move our attention from a small, poorly-led marae by ensuring something impressive can happen on the Treaty ground where history speaks and all should listen. This prime minister should at least make an attempt.