When the user navigates the tree using keyboard selection, sometimes you want to update the SelectionModel as they navigate, but other times you want to wait until they press enter. For example, if the tree is serving as a left nav menu, you probably don't want to switch screens in the content area every time the user presses the down arrow on the keyboard. At the least, it might be expensive or slow to select a new object. With KeyboardSelectionPolicy.ENABLED, the user can move around the tree without updating selection.
I agree with Brian that the aria role should match the tree CSS, so it should go in keyboardSelected(). As far as issue 7480, it sounds like a bug. Updating the SelectionModel should update the CellTree's keyboard selection. http://gwt-code-reviews.appspot.com/1776803/ -- http://groups.google.com/group/Google-Web-Toolkit-Contributors
