For me I think ones level of success depends on a number of factors.
Personality: I think physical attraction catches the eye but it is ones personality that will hold there attention. If one has an undesirable personality or lack of personality no matter what looks or money or other factors they possess in the end it will become in vain because the other will eventually tire and move on.
Geographical location: I think many people deep down would prefer to meet somebody within a certain distance and not have the inconvenience of traveling back and forth for a relationship, so success depends on the number of people within this desired area. Geographical location is less relevant to those who want to date but for those seeking something more longterm it does become an issue.
Freedom to move: Most people have roots let it be career, family or other commitments and for many to start over again in a new environment, it is not the most pleasant issue to contemplate and sometimes not possible and notwithstanding the fact that the person would have to be extraordinary in the first place to even contemplate this, as they would say from a marketing prospective they would need to resemble a monopoly where there was no substitute product.
Never give up: For those who indeed find success from internet dating, this seems to be the most common piece of advise. For me this is a poison chalice, we are human and we often read into things. If a person informed you they had been a member of a site for e.g 5 years, it is unlikely too many would see this as a great commitment on there behalf to find love rather people could potentially see this in many other less positive ways.
I would love to hear other people's views of what determines success through internet dating.