Heh, "regular Jon Doe who uses office and surfs the web a bit won't feel a benefit from more thorough defragmenting, so we won't do it at all" - way to go, Microsoft.
Proper defragmenting certainly is noticeable for the rest of us. Large game data files, virtual machine disk images, etc... And do try burning a heavily fragmented DVD image and watch the buffer indicator while doing so...
Craptastic.