Yes, they do, provided they have some integrity -- which all of the people that I work with do, they have all been introduced to me by a very successful internet marketer who also teaches people the exact formula he used for success. The mistake in your thinking, I would say, is the assumption that it would be a) easy, and b) anything you do would be direct competition to them. Both are false. Your own success will not impinge on their own, it magnifies it. Also, while the methods are generally pretty simple, they're not easy -- and the vast majority of people simply aren't willing to get off their butts and put the information into practice.
They benefit when you are successful because it brings them a lot of word-of-mouth, and helps them develop a great following. If you have ever actually worked with these people in one of their programs, you'd know that most will bend over backward to spoon-feed you every possible thing so that you can be successful. Many even put all of their information into their books as opposed to a training program, because they know that some people can learn and be successful that way -- while the vast majority needs hand-holding to do it. They liken it to college textbooks -- all of the information you need is right in front of you, yet most people still feel the need to go to class even if the teacher doesn't require it. Ultimately, it is still up to the student to actually use the information.