What difference does xargs make here?

What is the difference between

find / -name 4000 2>/dev/null | ls -l
and

find / -perm -4000 2>/dev/null | xargs ls -l

The only one I noticed is the first one just gives the output as total 0
and the second one lists files as the ls -l command does. Why the output of the subcommand before the pipe symbol in the firs case is given as argument to ls -l but it does when using xargs.