This stuff simply makes it very difficult for water to stick to a surface. So water won't stick to the fibers of fabric. Water can still get between the fibers. Once it does, it will make it all the way through and you will get wet.
If water hits a sweater treated with this stuff most will roll off. However if it lands on a flat surface such as your shoulder it may sit there. Then when the next rain drop hits the first the resulting pressure will push water between the fibers. Any more rain drops that hit will drive the water further through the fabric even though the water is not sticking to the fibers. So a sweater treated with never wet will stay dry but water will still make it through to your skin. It would take longer but in the end you will get wet. Fleece would be the same.
A very smooth surface with densely packed fibers (nylon or similar fabrics) treated with never wet would work better but there is still space between the fibers. space that water can occupy and move through.
think of it this way. A bucket made from never wet treated fabric will hold a some of water but as more and more is put inside the pressure will eventually force the water into the space between the fibers, and eventually out the other side. Once one drop makes it through the rest will follow. The water won't stick to the fabric but it will stick to the water in the spaces between the fibers.
It was mentioned that a cell phone treated with this still worked after being submerged 1 foot in water after 30 minutes. This however is not a very impressive claim. for starters many printed circuit boards are now coated with a varnish or paint after assembly. This is done to keep it clean and dry. A well designed product would also have a gasket between plastic parts and buttons. Take the same treated phone and place it under 3 feet of water and it might fail in seconds due to the pressure driving the water in.