[CentOS] OT -- BASH

Can someone explain why this:
   find . -depth -print0 | cpio --null -pmd /tmp/test
will copy all files in and below the current directory -and- this:
   find . -depth -print | grep -v .iso$ | wc -l
will count all the non-iso files -and- this:
   find . -depth -print | grep  .iso$ | wc -l
will count *only* the iso files -but- this:
find . -depth -print0 | grep -v .iso$ | cpio --null -pmd /tmp/test
doesn't copy *anything*?   
Any suggestions for a work-around would also be most welcome.