may be people are not satisfied what they have our what are they. People became envy to the other because they want to experience the things they have or may be because it is they dream to be like the people where they are envy^_^
No one in the world will be ever satisfied with what they are having. They will always try to get better things in life. I would not say that this is a part of jealousy, but if someone is lacking something which his neighbor is having, then he may be feeling animosity towards that guy.