Most people who care about such things know that you can press Ctrl+Alt+Del twice from the Welcome screen and sometimes you will get a classic logon dialog. (Note: "Sometimes". It works only if the last operation was a restart or log-off, for complicated reasons that are irrelevant to this discussion.)
The ability to do the double-Ctrl+Alt+Del was added as a fallback just in case there turned out to be some important logon scenario that the new Welcome screen failed to cover, but which the designers had failed to take into account by simple oversight. Scenarios such as smartcard or fingerprint logon.
In other words, it's a kludge.
In the time since Windows XP came out, the logon folks have kept an eye out to see if there indeed were any scenarios that weren't covered by the Welcome screen. I think the only one that came up was Kerberos authentication.
Now that (once they fix the Kerberos problem) they have covered all the bases, the designers are probably going to feel more confident about the new logon design, and the double-Ctrl+Alt+Del panic button will likely be removed.
So don't get too attached to it.
This is why the Welcome screen shows that Administrator account if there are no other members of the Administrators group on the system: If it didn't show the Administrator account, you would be locked out of your own computer.
"No I'm not. I can use the double-Ctrl+Alt+Del trick to log on as the Administrator."
Well, okay, that works today, but you're relying on a panic button that might not be there tomorrow.
[Raymond is currently away; this message was pre-recorded.]