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Thom, your article is slightly inaccurate as it deduces that the the traditional desktop shell is not an application when in fact it is (it's just explorer.exe).
In fact you used to be able to change what app to use as the shell quite easily in system.ini (change the value "shell").
After a quick google it seems you can still replace explorer.exe as the shell even on Win7. The setting is now in the registry:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon Edited 2012-05-15 09:38 UTC
exactly what I'd already said - 'cept yours was the "concise" version..
Regardless, the new Start screen, charms, etc. can't be a replacement for explorer.exe because they are part of explorer.exe. They are not a new shell, but rather just a set of new features added to the existing shell.