Expect the unexpected. That was the mantra that won the 2011 World Cup for the All Blacks, according to their coach then, Graham Henry. By naming only two hookers for the 2015 World Cup is Michael Cheika challenging this mantra?
Henry's strategy of expecting the unexpected came out of a review of the All Blacks failed 2007 World Cup campaign. Going into the quarter-final against France, both No.10s, Dan Carter and Nick Evans, were injured. Plans were made for this never to happen again. When Dan Carter ripped his adductor tendon off the bone before the final pool match against Canada in 2011, Colin Slade was brought into the starting line-up. Slade was then injured. Aaron Cruden, another playmaker with Test experience, was brought in and when Cruden was injured in the 33rd minute of the final against France, Stephen Donald, wearing a jersey that exposed his mid-riff, came on and kicked the winning penalty. 
The point here is that Donald was playing his 23rd Test for the All Blacks during the final. As a comparison, Bernard Foley, the likely starting No.10 for the Wallabies, has played 19 Tests.
During the 2011 World Cup, Robbie Deans' Wallabies carried only one genuine No.7, David Pocock. Pocock suffered a back spasm in the final training run before the crucial pool match against Ireland. Ben McCalman, a blindside flanker or No.8, replaced him. With no one challenging the Ireland loose forwards for the ball on the ground, on a rainy night, the Wallabies were bustled and harried out of the match. The unexpected loss, Australia's first to Ireland in a World Cup, meant the Wallabies went into the All Blacks' half of the finals draw.
Rupert Guinness ran an interesting interview this week in The Sydney Morning Herald with Cheika's Argentinian set-piece coach Mario Ledesma on why there are only two hookers in the Wallabies World Cup squad. "If we have an injury that lasts only one week we just get the other hooker [James Hanson] who has been training with us," Ledesma insisted. Sorry, this can't happen. If a new player is brought into the squad, someone has to drop out. Ledesma hinted, as well, that one of the props could play as a hooker reserve. That prop is Scott Sio. According to World Cup rules (1.1.7) teams have to present six front row players for a match, even if there is a last-minute injury. With a once-in-a-decade series of injuries, at the wrong time, the possibility of a default comes into play.
Stephen Moore was injured in the first minute of a Test last year against France. Tatafu Polota-Nau, with his kamikaze tackling style, is frequently concussed. The Wallabies, too, have an "awkward" (Stephen Larkham's word) World Cup schedule:   September 23 against Fiji, going to a   September 27 match against Uruguay, and then to   October 3 match against England. The chances of both Wallabies hookers and props emerging unscathed are not high. Will Skelton and Kane Douglas went at each like pit-bulls this week during training and had to cool off. Can Moore or Polota-Nau be quarantined from this mayhem?
Wouldn't it have made more sense to take a third hooker and not select one of Henry Speight or Joe Tomane?
There were calls for Dylan Hartley to be selected in England's 31-man squad to restore the side's traditional bully-boy dominance. Hartley, though, is under suspension. He couldn't play in the World Cup until after England's opening match against Fiji. England ran the risk of breaching the World Cup rule (1.1.7) if the side presented only two hookers before the Fiji match. So England have disregarded Hartley for three specialist hookers. Memo to Michael Cheika: Expect the unexpected.