I've heard this about Navajo rug weavers, but not for the "Only God is perfect," reason, but rather, that the slight imperfection allows the "spirit of creativity" an escape route, so that another rug can be woven in the future.

And, regarding the deliberate asymmetry of Japanese pottery: Can that really be counted toward "imperfection," if, in that asthetic, symmetrical is boring (and I think I agree, on that point)?