Barry, that was my first thought, too...but since Tasks on Projects can be deleted and inserted, the WBS can differ, even on Projects that originate from the same Template, effectively mixing up the comparisons.
Another way then, Alyson, is to group by the Template Task's Task Number, which (within a list of Projects based on the same Template) will always give consistent results (provided the Template stays the same).
(Sidebar: if Templates do change, by the way, you can synchronize the changes out to existing Projects using our "http://store.atappstore.com/product/sync-template/">Sync Template AtApp.)
That all said, though, I would encourage you to consider using Milestonesh to allow for comparisons between similar Projects that might not have the same Template (or any at all).
Regards,
Doug