I just found this question and was searching for the same thing.
In Explorer in Windows 8, if you press enter while in the address bar, it goes directly to the file list.
Unfortunately, the behavior is not the same in the file open dialog, even though most of the shortcuts there are the same.
You can easily get there from the find dialog: if you press F3, then ESC, then down, you will end up in the file list (both in Explorer and the file open dialog). Unfortunately (and bizarrely), however, F3 doesn't always take you to the search box. It depends on what element you have selected at the time.
It is amazing how poorly thought out the Explorer shortcuts are. There are direct shortcuts for most elements in the interface, including rarely used options like Map Network Drive--but not for selecting the file list!