I have heard people say this before, and it always makes me wonder. Why not remember it as "extract zipped file" instead of "extract zee file"? That is after all a more accurate description of the flags you are giving tar, z indicating that the tarball had been gzipped. You can also specify j for bz2, and J for xz (sorry I don't know any cute sayings for that).
Of even more interest to you is probably that with modern version of GNU tar, you can just say tar xf filename, and then tar will automatically determine whether it should use gzip, bzip2, or xz based on the filetype. So you can save yourself an extra letter there.
