Some people really do need to take the name brand even when a generic is available. The active ingredient is the same, but every drug has "inactive" ingredients as well. Those inactive ingredients are still chemicals (everything is a chemical of some sort, even your food and the air we breathe), and there's certainly the potential for those inactives to somehow affect the way the active ingredient is taken up by your body and how it works once it's there. Also, the way the generic is made, the processing, may have slight differences that affect how the drug will work.
Same with the latest and greatest. Sometimes newer drugs are needed.
Just realize that this isn't always the case and don't accept a prescription for the most expensive thing without at least discussing it with your doctor. They rush through their 15-minute visits, doing medicine-on-the-run. Sometimes they need to be questioned and think about why they're prescribing something. It shouldn't be because it happened to be the brand they just heard about from a drug salesman.
Btw, new drugs don't have generics because of copyright/patent/trademark laws. The drug company spends a lot to research and design new drugs, so they get that monopoly on thier inventions for the first however many years. And, granted, they take full advantage of that and charge the earth.