I think what happens is that Windows switches to desktop whenever a desktop app is started. However explorer detects when another instance already runs, and just exits. The end result is what you want.

However while I don't like Metro, it's a single click to get to the desktop.

For some reason I don't want to get involved in hacks to make Windows work the way I want to. For one, it forces me to accept the changes that I eventually need to accept, no matter how counter-productive they are in practice. Second, any hacks could interfere with future changes that MS makes. For instance, what happens to those hacks if MS ever decides to restore some of the previous functionality? Would they conflict?

EDIT: Actually the second instance of explorer does not exit. It opened a Windows Explorer window, but the 1st one was behind some other windows so I didn't see it. So with the proposed hack you have an explorer window open. So either way you need one click to get to a "clean" desktop. Maybe a tweak could be to run an empty batch file or something instead of explorer.