It is true that photography is (or at least can be) an art form, giving it a wide range of interpretations. What I think distinguishes it from other visual artforms is that it is an artform that is grounded in the natural world. In other words, nearly all photography begins with an image of something from the world, not from someone's imagination, or something derived from a mathematical algorithm. And I think it is this connection to the natural world that makes photography so powerful. It's history as opposed to fiction. It's "based on true events" instead of "original screenplay". And it's the combination of truth and beauty that makes great photography. When there is too much manipulation of the original image, the photograph loses believability. Not all photographs need believability to be great, but those probably wouldn't be my favorite photographs.
I also agree with the statement that digital photography didn't introduce manipulation of the image. It went way passed dodging and burning with film. Just look at some of Man Ray's self portraits.
http://www.noreascon.org/retroart/im...20Portrait.jpg
There is definitely some abstractness there. Many people think these photographs are great art but I don't really like them.
I want to point out that everything said above assumes that the photographer is an artist. There is also the view of photography as a craft, where the photographer is just trying to create something decorative or useful (think documentary) instead of trying to convey an idea. This is generally the way I approach my personal photography. In this context, too many photographic tricks can be seen as a crutch. The photographer can't figure out how to make a subject interesting so they use some HDR techniques to make it "pop". A lot of it comes down to personal taste so feel free to disagree with any of my points.
I would encourage people to visit the blog,
The Online Photographer. A few months ago there were several posts dealing with these sorts of issues. Browse through the November 2007 archives and you should find it. It is very intelligently written and it helped me think through a lot of these things.