I just think he cant play there, Gambhir put up a crap load of runs in that series and Sehwag failed. He still doesn't have a 50 in New Zealand.
New Zealand pitches or conditions offer some movement and if a bowler can get some movement in the air or of the seam Sehwag is screwed. It wasn't his "idiocy" it was just the lack of skill and will do adopt to different conditions. He can put up with a little bit of extra bounce but against swing and seam he is like a fish out of water.
When India toured New Zealand earlier this year the pitches were as flat as I've ever seen them, Sehwag like Stinky stated was just trying to thump everything out of the park, he undone himself more then anything.