When designing shelves of this nature, the manufacturers understand that these shelves are hanging with no external support. Therefore, they are specifically designed to be reinforced. This is done by adding attaching screws into the wall and the internal brackets are made from durable materials. They are also extended enough to give excellent support. With this type of design, you are able to put heavy items on these shelves without worry.
Have you ever tried to install a set of shelves only to find that the brackets get in the way? No matter how you change it around, you just cant seem to get it right. There is a type of shelving that can help you avoid this problem altogether, they are called floating shelves.