I was wondering the same. I tried using a few of them over a period of time but after a while I'd lose the discipline and stop using them completely. I felt that instead of making me more productive, they were just introducing more overhead into my life for things that I was already able to handle by myself. I don't have a problem prioritizing and remembering tasks in my life, so apps like that end up being more expensive to me in terms of time and energy than using nothing at all. They just feel gimmicky. And if something is so unimportant that I can't remember I have to do it, then it's probably not worth doing at all.
As for the list... it's funny the way it caters mostly to iOS users. I understand that the journalist who put together the list probably uses a Mac and owns an iPhone, but this just reeks of unprofessionalism.
I'm not here to attack or defend to-do apps, but regarding your statement, the utility of software rarely comes from the specific things it can do, but how it does them. There's usually non-functional differences.
What can be done with Python that can't be done with assembly? Nothing, but (for most cases) you can do it quicker and easier.
What can be done on an iPad that can't be done with a desktop computer? I doubt there's anything that you can do on an iPad that couldn't be done, in principle, on a desktop computer. The difference is portability and stuff like that.
Whomever does this right will become dominant and make a lot of money. The closest I've seen is Any.Do and Omnifocus. The latter may be too complicated for the average user and it is a premium product.
