I was just reading this article where the author talks about the file system fragmentation that can be caused by growing database files. There was one bit that I didn't quite follow.

What about Windows defragmentation tools?

Although you can use a Windows defragmentation tool to defragment your database files, these tools simply move chunks of files around to get them contiguous. This moving of chunks of files can cause internal fragmentation that you might not be able to resolve easily.

Is the author saying here that the disc defragmenter makes no attempt to put the chunks of files in the correct sequence or have I misunderstood? If he is saying that then is this a limitation of all disc defragmenter utilities - even commercial ones?