What you've missed here is that despite the fact he "explained" The System, there is no guarantee that system would work. While the probability made sense to the nation, and they bought it, there was never going to be 100% odds that the last person would place a winning bet. It was still a mutually exclusive event. The more important part is that he deliberately took over from that person to place their bet for them(and he changed it), much like he took over to do the numbers on the Lottery prediction. In reality there's no probability involved at all. While he appears to explain things, and people have accepted those explainations in the past at least, he's actually given away nothing at all... Although that was painfully obvious with the Lottery one, it's was a little less obvious with The System. The System was still an illusion, and not actually down to the explanation he gave. This is why Joe Public seem to be upset by the Lottery stunt as they realise they've been fooled. whereas they didn't realise they'd been fooled with the System.