So, you have personally compared the two in pouring rain? Hey look, I'm not trying to win an argument. It's just that what you said is contrary to my experience. In my experience, a non-breathable poncho will keep me almost completely dry in the pouring rain, as long as I'm not running around and getting sweaty. In contrast, I do have some expensive Goretex jackets (not ponchos though) that will leak eventually. Again, I'm talking about pouring rain, not snow.

Here's an example of the non-breathable, waterproof material that I prefer in the pouring rain:
http://www.bicycleclothing.com/Waterproof-Rain-Jackets.html