As I mentioned in my edited version of the original question, this is a question that was presented to one of the other writer's groups that I am a part of, and I wanted to see what folks here thought of the issue. I thought I would go ahead and share what came out of the other discussion.
As it has already been mentioned, if you are under contract to a "traditional" publisher, the writer doesn't have much input on this decision. The publisher is going to do what they believe to be in their own best interests, and that makes sound business sense.
However, for a self-published author focusing primarily on e-books, it is a completely different matter. What most of them have decided is that it does not make sense to use DRM for their books. The reason, as mentioned in other answers here, is that they are more concerned about getting readers, so if anyone wants to share the book, they are okay with that. They feel that the possible benefit of obtaining a new follower outweighs the potential lost revenue.
To further expand on that, a good number of them actually offer at least one book for free in the express hopes that people will enjoy it so much they will go back and buy something else the author has available. In a similar vein, many will offer a loss-leader, or a very low priced book, with the same intention. Bottom line, for them it is more important to obtain a following.
Interestingly enough, we found that a good number of more successful authors agreed with these same principles. They felt that the need to continue to increase a following coupled with the risk of alienating some people by using DRM meant that it made more sense for them to NOT use it.