Because to succeed by breaking so late the other driver has to back off and let him pass, if the other driver keeps the normal line Koba could be out as almost happened the first time he overtook Alguersuari. It's ok to have drivers like him but I think it was much more about a faster car and gambling than driving skills, for each race like this will have another where he will DNF.
It clearly wasn't so much of a gamble that he couldn't do it several times at the same corner... he braked later than anyone there, and also did that on a tighter line... that takes guts, talent and good foresight. So what if he's putting his faith in the other drivers seeing him coming up the inside so late... they all did, and only Alguersuari made it dicey by acting like an idiot (actually he reminded me of an AI car in a game, forcing itself back onto the pre-determined line) on the corner exit. Kamui demonstrated that there is a gulf in class between him and the other rookie drivers at this point.