Ranking by the market cap is coming from traditional markets. I hope we will find another ranking methods to sort crypto currencies.
It's a fairly old ranking method, but it's the most effective one I know of... It would be awesome to find a better method, but I doubt that's gonna happen anytime soon.
We'll have to cope with the current way of ranking. It's not always as handy as we may want it to be, but overall, it offers the highest reliability of all methods I've been presented.