Experimented? No, they inherited it from UNIX, that's how you do it there. UIDs are not necessarily human users, they are likely to be applications. Look at Pos

Experimented? No, they inherited it from UNIX, that's how you do it there. UIDs are not necessarily human users, they are likely to be applications. Look at Postfix, OpenSSH, vsftpd, or any other software that bothers to limit its capabilities. They all have allocated UIDs in the system.