I have to add here that eNotes.com is by far the absolute BEST website I have ever encountered for help with literature, history, and many other subjects. I tell all of my students about eNotes because it is reliable, credible, and accurate! I am blessed to be able to work for them as an editor here! :-)
Enotes is a self-sustaining company, as implied by their name: Enotes, inc. The group is based out of Seattle, Washington, and while they do accept advertisements from third parties, no one particular outside organization is solely responsible for its operation. Advertisers, in many cases, support the role and mission of enotes, but they are not its foundation.
Much like Microsoft, Apple, Coca-Cola, and other corporations, enotes runs its own business within the confines of regulations and other guidelines. Hope this helps -- if you have any further questions, check the "About Us" section of this website.