The main question is this: If I was writing a wiki engine and wanted it to be compatible with other wiki engines, why would I implement Creole instead of, say, MediaWiki syntax?
It's easier? ;)
Easier to use or easier to implement? If you mean to use, then I don't see how - most of the differences between it and MediaWiki appear cosmetic. If to implement, then I'm no expert on languages and parsers, but based on the discussion in this thread, I see no reason to believe Creole will be easy to implement.