You mean, wikis wouldn't be possible if filesystems weren't case sensitive? Come on, you don't believe that. Just that some wikis exploit both the mapping some HTTP servers make between URLs and filesystems, and the case sensitivity of filesystems doesn't mean wikis are otherwise hard. Take a look at one of the larger wikis: wikipedia. It's database driven, not filesystem driven, and hence, neither depends on the case sensitivity of a file system, nor exploits it.

There are many good arguments for a case sensitive filesystem, and I'm glad I don't have to work often with filesystems that are case insensitive, but I don't think "wikis" is one of the stronger arguments.