The issue is that the zone is only one factor. Being in the zone only implies that ONE criteria for life as we know it has been satisfied. It says nothing about the likelihood of it being inhabited. In addition, the zone was a very, very early rough estimate about where life might be possible. As we learn more and more about where life actually exists we are discovering that the zone may well be totally irrelevant anyway.
well the planet also has to be big enough to support an Atmosphere this one is bigger than the erth so loads of atmosphere for every body, from what we know wather is a key factor (there are extremofiles that live in acid but they are one cell organisms) so the zone is a good bet to look for complex life cause it alowes water in a liquid form.
what else you need for complex life is a good question? on earth we see that life fills every nook and cranny and it uses everything at its disposal.