A lot of this depends on whether you're crossing devices. If you think of drive letters as mount points it may make more sense - if you're moving between mountable filesystems obviously a move has to be a copy-then-delete; if you're remaining on the same filesystem a move can typically be a rewriting of indexing information only with very limited data rewriting.
One other thing that can be an issue particularly on NTFS with ACLs is that moving files typically retains their ownership and permissions, while copying files typically inherits the ownership and permissions of the destination. This can bite you if as an administrator you're moving data from one user's account to another because a move will leave the original owner still owning the files.
One other thing that can be an issue particularly on NTFS with ACLs is that moving files typically retains their ownership and permissions, while copying files typically inherits the ownership and permissions of the destination. This can bite you if as an administrator you're moving data from one user's account to another because a move will leave the original owner still owning the files.