David Lloyd on the Crowd Goes Wild Breakfast: Fantastic bowlers being left out
"They have still been brilliant in the group. They understand that as best we can we're picking the side for the surface and the opposition to give us the best chance of success.
We've got all 15 players on board with that," Williamson said, describing Boult and Southee as "very much ready to go" should the pitch demand: against Sri Lanka here on Saturday, England bowled 16 overs of pace.
In lieu of the two pace bowling kingpins, New Zealand's success has been underpinned by spin bowling: a startling turn of events for a country not renowned for its tweakers.
Read more: England v New Zealand
Williamson ready to replicate Kohli, Root
'I'm putting the ego aside', says Colin Munro
Mitchell Santner and Ish Sodhi have so far shared 17 wickets at under ten runs apiece, each marrying turn with remorseless accuracy and displaying a sterling temperament.
"Spinners have been brilliant on surfaces that have suited spin bowling. Even when we've played on perhaps the best track we've played on, which was Mohali, they still played a big part."
Flexibility has been another hallmark of New Zealand's success in this tournament. The presence of Grant Elliott and Corey Anderson has provided depth with bat and ball alike, and allowed Williamson to adapt his plans under pressure.
"Things can change so quickly that its important that allrounders are a big part of the game - you can call upon guys to bowl an over or two that have slightly different skills to one another. That can make a difference."
Listen to Kane Williamson ahead of the World T20 semifinal:
Just don't call Williamson's side favourites. "It's almost impossible to give someone the favourite tag in T20 cricket, it's so fickle in nature." One obstacle for New Zealand could be batting second: Williamson won the toss in all four Super 10 matches to set up victories defending targets.
The venue for the match might also be to New Zealand's disadvantage. While England will be playing their third consecutive match at the Feroz Shah Kotla in New Delhi, New Zealand will be playing here for the first time in the tournament: it will be their fifth different venue in five games.
"We've been able to see more of India than most opposition sides," Williamson joked. "The guys have embraced it, embraced the flights and the variety of the hotels.
"I suppose England have been fortunate to play in these conditions a couple of times but I think in Twenty20 cricket anything can happen. It's an exciting occasion tomorrow night and one I'm sure the guys look forward to."
When he walks out to toss with England captain Eoin Morgan, Williamson will encounter an England side who bear no resemblance to the rabble pulverised at the Cake Tin at the World Cup 13 months ago.
"I can't quite believe how far we've come overall in our white-ball cricket," Morgan said, while stressing that England are in New Zealand's debt. "We talked about emulating what Australia and New Zealand did at that World Cup. From where we were to where they were, we were miles away. In order to bridge the gap we had to try and emulate the fashion in which they played and the aggressive nature in which they went about their game and particularly with the ball."
Williamson will hope that he does not find England too inspired by the Black Caps.
