Wiki searching has always been really crappy. You have to get the spelling right and you can't use small words.
In your case, I suspect you're running into a limitation with earlier versions of mysql where fulltext searches required a minimum of 4 letters. In building it's index, mysql threw out all 3-letter and below words to reduce the size of the index. The side effect is that "G5" and even "Mac" aren't searchable.
(Now, this is only a theory, as I haven't dived into the wiki code very far. Also, newer versions of mysql fix that issue).