Bhoy, think of it like what they do with pooling health insurance in the US ... you all pay the same fee in your pool, but only some of you are going to get ill and actually have to draw money out of it. At the start of the show, the BBC now thankfully has something of a rule book in place and this rule seems to be in it ... any contestant ruled out by a doctor from dancing can skip one week only and continue in the competition. At the start, all know that person might or might not be them. Indeed, one of the others could get injured next week, and they'd get the same break. It doesn't only become a fair rule if everybody gets injured and gets to skip a week.