Yes, I have now gotten this to work... on OSX (as in other platforms), you ctrl-click the project icon itself at the top of the Projects list.
It would be nice, however, if we could do that on the Project icon of a specific project (that has sub-projects, of course). I think this actually would be a more common use of this feature... it's unlikely I want to expand-out all my projects and sub-projects (although of course it's nice to have this feature).
However, being able to do this on a project folder would be superb... then I can go to just a specific folder (House) and ctrl-click THAT, and see my subprojects (Get New Roof, Maintenance, Refinance Loan, etc.).... all expanded out and any sub-sub-projects, etc. But not see all my other top-level projects also expand out.