Presuming you're talking about WinNT and derivatives (2000, XP), I recently learned that NT's filesystem supports finer control over permissions. It's possible, for example, to grant only a specific user certain permissions, or restrict some user from permissions. To do something like that with ext2/3, you'd have to do some weird group stuff, making it pretty hard to do.
Maybe some of the other filesystems supported by Linux would give that kind of permission control? (Dunno, I haven't tried them.)
Though, as everyone else has pointed out, you can use the "sticky" bit to do what you're describing:
chmod g+t directory_name
Read the chmod manpage for more details.