I think "untitled" is probably the result of the person at the gallery labeling the image, rather than the photographer actually titling it "untitled". It's like there is a blank line that must be filled out; rather than an absense of a title, the gallery needs to let us know that the photograph is "untitled".
I was going to say that I don't give my photos titles, but then I realized that I do usually write something when I post. I guess I think of it more like a caption: "Maisy at the slide", "Black Rock", "Wetlands Grass". A lot of my landscapes have the same title. I'm putting together a landscape portfolio right now, and all dozen or so photos have the same title: Douglas County, KS.
Titling my work isn't real important to me. Dramatic or philosophical titles is definately not my thing. But each image needs some sort of identity so I can keep track of it in files, darkroom notes, conversation....