Can Agile be accomplished without client involvement?

Question

I couldn't write a book on Agile. I have worked in several shops that call their process Agile. One of the main points of Agile development is regular client involvement. After a sprint, the work can be demo'd to the client to obtain their feedback. Rinse and repeat.

The problem I come across is that many clients do not want to be that involved. They would much prefer a waterfall approach. Gather the requirements up front, then come back when you are done. In my experience, waterfall does not work. Clients do not know what they want until they see it. The waterfall dilemma is further propagated by a large community of developers that want to have all the requirements up front. This way they know what they are building, they can architect accordingly, and the client is to blame because they "signed off" on said requirements.

Am I incorrect? Can Agile work without client involvement? If so, how and how do you overcome the issues I discussed?