Yes, the escape key does work, but you sometimes have to hit it multiple times to get back to the main form. I also know I can just click it in the treeview in object inspector, but if you have a lot of stuff on the form you have to scroll all the way up and then click it. Having it select it in the treeview when you click the title bar is nice and fast with a single action, all the other ones involve multiple actions to select the form so it's events and properties show in the object inspector.
In all versions of Delphi single clicking the title bar also directly selects it in the treeview in the object inspector. there is no reason clicking the title bar could not also select the form in the treeview in the object inspector.
I files a bug report in the Mantis tracker.