Sure. Typically they are specialized in a single type of content. For example, JSTOR is a self-described "digital library" which provides journal access. Your local movie rental store (or its competitor Netflix) provide entertainment or educational content (movies and shows).

Of course they can be regulated just like any business or service. So could this service, in fact. Forcing net neutrality for all service providers would cut out a lot of crap and I'm convinced it's a long-term boon.