This is true. When I was younger, I was of the opinion that people should not judge you by your appearance. While this is ideal, it is not how people behave. Appearance makes a difference in what opportunities people offer. If you are going to associate with them, they want to know that you will represent them well. Furthermore, if you do not care for yourself, you will likely not care for them and their interests.
Taking advantage of the prejudice of appearance can work in your favor if you dress well and present yourself well.