[Publius6961]

PKZIP is a popular program, but is becoming less common, such that not many people

Wrong!
PKZip has become more popular since worms and viruses became universal.
Many web sites routinely reject any file with the .doc extension; making it a zip file is the only way Word documents can be sent in that case.

[PatrioticAmerican]

web sites might reject docs, but they are onto the zip thing now as well, refusing any attachment.