Put it this way: Comcast owns NBC Universal and its programming. So when you're streaming Parks and Recreation reruns on Hulu, complete with advertising, they're making money from you. They're not going to do anything to hinder your Hulu streaming experience.
You watch one episode, get bored, and decide to start browsing MacRumors. Comcast has no stake in MR and makes no money off of it. Without Net Neutrality, they could slow down access to MR to the point where you're like "Damn, this site is completely unusable. I guess it's back to watching Parks and Rec" - unless you pay more for unrestricted access to sites. Or if MacRumors paid a ransom to Comcast to unrestrict their site for all Comcast customers.
No NN would almost allow them to set up speed tiers for different sites: You would get 50 MBPS for Hulu and anything else that makes Comcast money. 25 MBPS for Netflix because Netflix paid a ransom to Comcast. 10 MBPS for Twitter because Twitter also paid a ransom (but not as big as what Netflix paid). 5 MBPS for almost everything else. 3 MBPS for Amazon because Amazon told Comcast to take their ransom request and shove it up their arse, which angered Comcast, 1 MBPS for Skype because it competes with Comcast's landline services, and dial up speeds for AT&T and Verizon's site because they don't want you checking out the competition's pricing.