That's the way percentages work. For example if there are 100 bottle caps and you said you had 99.999% of bottle caps, you really have 99 bottle caps and MOST of the 100th. But you could say you have 100 bottle caps just cus. 

In the same way, is the above. You're not REALLY better than 99.whatever percent of the population because you can't be better than MOST of a person like you can have MOST of a bottle cap. But if you take (X-1) and divide it by X where X is how rare your skill is as a representation of 1 in X then multiply by 100 that's the percentage you get. In reality, it's irrelevant past a certain point because the decimals become negligible due to how small of a difference they make as a proportion of the population. 

EDIT: My point is that the percentage above are mathematically sound(if I got my decimals right) but it doesn't really matter