OS X and Linux case sensitivity are based on the file system, and configurable when defining/formatting the partition on the drive (if the file system itself supports case-insensitivity, since most do not).
Some FTP clients include an option to convert the filenames to lowercase. It may be the case that some hosting providers have a web-based file uploader which automatically converts filenames to lowercase as well.
As Narf already said, converting the filenames to lowercase is crazy, and I would put it at a level only slightly crazier than case-insensitive filesystems.
