Dietary supplements have gained a lot of popularity and talks in recent times. We get to hear and read various views on it. And these views at times also contradict each other from time to time. Without any doubt, it's a huge market at present. Many celebrities even endorse for them. And then there are studies to show that they if taken in excess can be as bad as deficiency. 
So, I totally agree with your statement. They are not a replacement for healthy and balanced diet. They should be taken under a medical supervision..the amount ( dosage) and the duration for which they should be taken has to be decided by the doctor. Consult your doctor before you decide to go for any over the counter supplements.