DOS' original COPY command wasn't too shiny: It could copy a file to another place, or concatenate two files, but that was just about that.
XCOPY was introduced around DOS 3 (I think, /msg me if I'm incorrect) and it gained new features later on.
It can copy whole subdirectories (switch /s), copy files with Archive attribute set (/a), files modified after certain date (/d:date), and create target directory automatically (/i). There are other switches, but their usability is limited.
In Win9x this command is actually called xcopy32, I think...