Using win+tab (what you call the metro task switcher) all desktop applications appear as a single item. 10 desktop apps running? Still, just a single item in the list - "desktop".
Using alt+tab (what we use in Windows 7) all desktop apps appear individually - including Store apps (what I am sure you would call metro apps). This is the way it works (even if it seems a hair inconsistent). alt+tab is certainly the superset of the two commands.
If you want to task switch between all your desktop apps, alt+tab is the only way to do it. Otherwise, your desktop apps appear as one item. That's just the way it is.
I hope this helps.