More or less, tar is like ZIP - an archive of files, whereas cpio is more like a volume backup. Cpio is probably not as popular as it used to be, although Oracle has been known to ship in cpio format. Tarballs can be unpacked by WinZip, but as far as I know, not cpio archives.
If you Google for "cpio vs tar", you'll discover a number of comparisons that people have done between the two.
Customer surveys are for companies who didn't pay proper attention to begin with.