There has been study after study showing how the wiki markup syntax is a hurdle to participation on wikipedia, to the point where wikipedia is now finally, after 12 years, working on a wysiwyg editor: http://techcrunch.com/2012/06/21/jimmy-wales-on-new-editing-...
There are so many free and open source wysiwyg editors that can be easily plugged into a site: aloha, tinymce, ckeditor, etc.