The official way is WikiPublisher, but for convenience (laziness) I often write Wikipublisher.
The small caps rendering on the wikipublisher.org
home page is a piece of typesetting bling. When the first letter of a book chapter is a versal (in this case a drop-cap), it is common practice to set the first few words of the first line in small caps. See Bringhurst's The Elements of Typographic Style, 2nd ed. pp 63-65. The lettrine package in LaTeX provides the print equivalent.
I would not write it in ALLCAPS; the small caps version is a consequence of its position as first word and the chosen presentation style for that page.
Hope this helps.