i think the 'squeeze the tank' bit sounds like a bit of advice from someone's book, twist of the wrist or the like. i think thats more advice given in 'riding for dummies,' mentality. a horrible habit to get into while under braking is sitting too far back in the seat..once you brake you slide forward on the seat, abruptly hit the tank, and unsettle the suspension under braking.
so i think squeezing the tank is just to get riders out of the habit of sitting back on the seat, and letting the suspension work more smoothly, and thus more quickly. obviously pro's have got it figured out, and do it properly without the mental note, thus they setup however they're comfortable going into the corner and rest up against the tank before hand.