Not really just about that, there's actually more to it. High-paying keywords, and/or tonnes of traffic. The right parking company that lets you customise your templates at least some. And there are a *lot* of sleazy or fly by night parking companies (sedo and parked are not, there are others that are legit, but there are many that are not).
Also the volume of business you do with a parker can get you better treatment, and some parkers can help you with one-click templates, and so on....there's a fair amount to it, and you're losing a cut of the money in exchange for some convenience....but for some names it could be lucrative.