Saying 'diet' is just a shortened form of 'slimming diet', or 'weight loss diet', or in the USA, 'reducing diet', etc. Over the years it has come to be immediately understood in the slimming sense unless specifically applied to animals or one's diet - food consumed - in general.
Finding the right diet for US, as individuals, is, I believe, what makes the difference. Atkins for example ticks all the boxes except fast weight loss. And for those of us sensitive to carbs (I sure am!) Atkins also offers the perfect maintenance plan. It's a continuum from Induction (Phase One) to Maintenance (Phase Four), all carefully planned and laid-out for us in the books and on the Atkins Community site.
Slimmers are not known for their patience. We hate being fat so we want the fastest results humanly possible. This generally means using a VLCD. Once we get used to the sheer speed of VLCD losses it can be difficult to impossible to 'settle' for the much slower losses of not only Atkins but also WW, SW, Rosemary Conley, etc.
What makes Atkins special is that it offers a healthy, uncomplicated way of eating and living that allows us to eat real food in moderate portions. All the way to maintenance and indeed for the rest of our lives. That doesn't mean that it is always easy to stick to! We are carb addicts and the old cravings will, on occasion, hit very hard. But even if we fall we can simply get up again, dust ourselves off, and get back on the Atkins wagon.
This is why Jim and others have lost so much weight and kept it off. Hard work, determination, and Atkins principles!