Everyone has a great set of abdominal muscles, yet most people have them hidden under a layer of fat. In many ways you don't need to exercise to get them as they're already there.
Burn away the fat and you should have an excellent flat stomach
The notion of exercises for abs seems to have been seriously plugged for years online and a lot of the advice centres on quick fixes which may not have a lasting long term effect.
The other negative is that the body is tuned into adapting to stimuli- after about 5 of the same workouts the effects lessen and a new angle/ alternate variations will be needed.
Also be aware of what a person needs from a program, big sets with lots of reps don't tend to build muscle size and there is a big difference between an abs exercise and a core exercise which will strengthen you functionally- I try to get clients I deal with away from lying down ab crunches as they have minimal crossover into daily life or many sports.
Be very careful of the information you take in on the Internet- just because its published doesn't mean it's right- we all know of hubs here which give bad advice and rank highly with google.