Some physicists have theorized that only universes in which the laws of physics are "just so" could support life, and that if things were even a little bit different from our world, intelligent life would be impossible. In that case, our physical laws might be explained "anthropically," meaning that they are as they are because if they were otherwise, no one would be around to notice them.Not belonging myself to the two categories Norm is addressing, I still feel a need to throw in my half penny.
On the physical front: the matter of uniqueness of relationship between physical constants' values and possibility of development of life is more in the mind of the physicists who support the thesis. This is something that is never going to be proved - only disproved, and it came very close to being disproved recently. And, by the way, it is not the physicists who should lead the investigation of the issue.
On the philosophical front: first of all, I would dearly wish physicists considered themselves a bit less of philosophers and a bit more of trained dogs that bring the philosophers new trinkets to get busy with. Some of the physicists succeeded in sitting in the two chairs, but most didn't. In any case, most physicists are sold on the positivism branch of philosophy. Their answer to the question about that tree falling in the middle of a forest will be uncomprehending silence: after all, if the fall wasn't or couldn't be measured by one of the senses and means available to science, what need is there to talk about it? It is just outside of the positivism's scope.
So yes, the anthropic (or, rather, anthropocentric, let's face the truth) explanation will be only natural to these folks. In spite of this, there might be countless parallel universes with the physical constants skewed a bit and still supporting life - as we don't know it. There might be - probably are - multiple populated worlds out there in our own universe, built on the same constants ours is. The lack of contact bemoaned by so many is rather obvious - just look at us...
More on anthropic principle here. And anyway, why don't I pass the buck to Francis?