Some of us just have the disciplines and desire to spend less than we make. It also helps a lot of you live in a low cost of living area, single with no kids and no bad habits such as smoking and drinking excessively.
For example: my rent (all by myself, no room mate) is less than $800/month in a nice neighborhood, even if I want to buy a house, I can get a nice house for about $200K. I cook at home and my meal is about $2/each or about $5/day or about $150/month. My car is several years old, is paid for so no car payment (and cheap insurance too) and I am going to drive until the wheels fall off. I don't have any cable tv bills, only $20/month DSL broadband. I pay about $30/month for cell phone service. I live close to work (5 miles or so) so I only fill up the gas about once a month for about $45, and on and on. I can say I can live with a budget about $1100 to $1500/month easily (good luck with pay the rent for that amount at places such as LA, NYC and such).
It is not how much money you make but how much you are able to save.