So the promoter announced the shows months ago but only just found out about the size of the stage and the fact that they can' get it from Wellington to Auckland in time? I highly doubt it.

I think it's a lot more likely that ticket sales would have been very disappointing. Mount Smart Stadium (the initial venue) holds 35-40,000 people for concerts whereas Vector Arena holds about 11,500 people during concerts. Consequently, had they sold about half the tickets of the stadium gig, they would have announced two indoor shows.

I must say, I never understood why they announced 2 NZ gigs and decided to have both of them on the North Island. Last time they played Christchurch (on the South Island) they had a sell-out crowd of about 40,000 people. Even Pearl Jam (with Ben Harper) only managed to sell 25,000 tickets and they're massive down there.