Player says that because it makes all the features visible, as most of you know. And, features that can't be seen are more difficult to factor into strategy, and not as attractive when you can't see them. We may be tired of the feeling that there is an absolute need to make every hole downhill, but it does have its advantages.
I think its a matter of percentages, not absolute. While you can all name great uphill holes, I suspect that if you went through Golf's Top 500 holes, most would be downhill or gently rolling. Player says they are "rare" which might mean anywhere from 2-10% of them, which seems about right to me.