"Neutrality proponents claim that telecom companies seek to impose a tiered service model in order to control the pipeline and thereby remove competition, create artificial scarcity, and oblige subscribers to buy their otherwise uncompetitive services." -from Wikipedia.org.
Basically, internet service providers want to pick and choose which websites you can visit with their service, hopefully prompting you to buy their service for content rather than quality.
I think it's important for Americans to think about net neutrality because all that information at their fingertips could fly out the window. People take a lot of things for granted when they get on the internet.
Links about the subject: