The navigation pane (tree browser on the left) works with single clicks. Of course, leaving that open does not leave much space for the center pane.
The problem with making single click open a folder is then you cannot select multiple items and it might confuse right click functionality. This is really optimized for desktop/laptop usage and needs to stay that way. The correct solution is to make a version optimized for a touch interface. I have a tablet myself so I have been meaning to do this...
I think I'll start working on a tablet version soon. I'll keep you posted.