Here's how I would break it down:
1. Image browsers - tools like BreezeBrowser that allow you to view your images, can be used to do light editing (rotating, renaming, etc), and could be used to organize your images
2. Image management tools - tools like iMatch, Cumulus to some extent, and maybe Exhibition Engine. These are meant to allow tagging, searching, viewing, etc. These are meant for organizing and cataloging larger collections of images. They may do more than this, such as editing, but the core competency is organization.
3. Digital Asset Management - very similar to Img Mgmt above, except tend to be used by groups of people, and also have a workflow component. May also include more robust transformation / conversion technology, i.e. the ability to automatically generate multiple different copies of a given asset, say a web-ready jpg and a print ready TIFF.
This is just my view of the categories, and you could probably argue that one tool could span multiple categories. For example, Cumulus bills itself as a DAM tool, but when used by a single person, I would look at it as more of an Image Mgmt tool since there would be less need for workflow / sharing.
BTW, tools in any of the three categories above could certainly include the ability to "share" images, either via a built-in searching interface, or via the ability to generate web galleries (such as Breezebrowser). The differentiator between 1 and 2 is more about categorization and cataloging from my point of view.