1) "Up" and "Plus" -- and "Down" and "Minus" are identical. The buttons were renamed from "Plus" to "Up" and from "Minus" to "Down" because the buttons on the new aluminum Apple Remote are no longer labeled at all. They were on the predecessor - the white Apple Remote. The new names, however, accurately describe the buttons on both the original and the aluminum version of the Apple Remote.

2) The OS X Apple Remote subsystem (and thus the Virtual Remote) knows no "Up (held)" or "Down (held)". It really only knows "Up" and "Down".

3) The pictured tour in the blog post you reference - in its last picture - shows you which actions to assign to the "held" entries for the Up/Down buttons: the same ones that you also assign to the "non-held" button states.

Best regards, 
Felix Schwarz