It's quite representative of the problem if you can't identify the difference between Wikipedia - a non-profit which is entirely ad-free and runs exclusively on donations, compared with the majority of other free sites which are funded by subjecting their visitors to advertising. No wonder Wikipedia has so to push so hard with its annual donation drives, if people can't even recognise the benefits of keeping it free from commercialism.

Hulu is an example which mixes both approaches - clearly an $8/mo premium subscription isn't enough to support their business model, so it has to be supplemented with ads. Not sure why this needs explaining. TV is obviously an industry very tightly coupled with ads, making it more difficult to disrupt with a fully ad-free approach.