The holes in the fabric don’t seem big enough for water to penetrate. Wouldn’t it be better if it were more open to let more water through?

The 5, 10, and 20-Year materials are patented products that are specifically designed to be just porous enough to let water through the fabric at the same rate that water is able to flow into the ground. If it were more porous, the water would just run off underneath the material. It would also let many more weeds through, and it would not retain the ground moisture as well.
Dalen’s landscape materials work many times better than the fabrics you may have used from other manufacturers that are much more porous. The features described are protected by U.S. Patent numbers 5,047,099 and 5,873,194, assuring you that you are using the finest product available on the market today.