My experience is that Youtube combats this (either intentionally or just by way of code changes) by changing the method in which the flv urls are determined by the player. The download sites break until they reverse engineer, and the cycle continues.
"PWN!" is a frequently used word on the Internet, the meaning of which clearly makes the words "PWN! YouTube" a parody.
"Mom can I go on pwntube to get a video for my homework?" "WHAT?!?! PORNTUBE!?!? NO!!!"
;)
Those who want their sites/products to go mainstream without ridicule (ExpertSexChange.com/ExpertsExchange.com is a popular example) or false negative impression/bias. This is why people often spend a lot of time to choose a name carefully, especially when you consider the long-term branding and marketing.
But this is a total misunderstanding about how piracy works. Someone will take up the challenge of breaking your DRM, and when they do everyone will download it from that person and then each other. DRM is completely ineffective in a situation where a single point of failure means total failure.