Hi Andria,
When you 'login as' you are masquerading, or becoming a user, this allows admins to login as the user without a password.
However when someone tries to login directly as a suspended user they will be denied access and an 'invalid login' message will be displayed.
You can test this yourself by creating a test user and suspending the account - then try a direct login. and also try 'login as'.
cheers,
George.