Um, seriously, yes, because formatting the drive creates your Fat & MBR and this is why the 'usable space' of a drive is always lower. An 80gb drive only gives you 76.x gb because the fat & mbr need to use space.
Your probably thinking that of the 'usable space' you probably want to make best use of it with the smallest sector size possible. This would be on ntfs 512 bytes so the most any one file will waste is 511 bytes and this will also add up.
This is why the 'space on disk' is always larger than the stated used space, no matter what format the dive is using.