Are there any hidden pages on the web ?

Yea, there is lots of places that is used between businesses and their clients. I've seen some of these, plus I use places on the internet for developing sites before I make them live for the clients, so those I also don't share with the other people. Except the clients get to see it, so they can be aware of the progress. But those development sites that I create are not available to the public either.

Sure it makes sense. LOTS of businesses these days use webpages to interact with their clients and their employees. There are multiple virtual telemarketing businesses that use people out of their home, and log in to a specific site where you don't have public access.