Why use linux tar.gz, instead of 7z or zip?
Because 7z and zip compression formats are not retained unix-style file permissions, for example, extract the executable file to be re chmod chown to return to normal. The tar format. The tar itself does not provide compression, nothing more than to include content and permissions of all files makes up a file and has been, so use another format such as gzip compression. Why is gzip, because almost all linux support only.
From the compression algorithm is, gz gzip is the abbreviation of, and zip compression algorithm used is Yi Luhuo.
In fact, Linux has a switch tar.xz, such as deb (debian / ubuntu with the package format) several years ago with the tar.xz. xz and 7z is Yi Luhuo.
If you care about is tar.gz is two, then the first tar gz, it is because linux unix philosophy by "a tool to do just one thing," impact.
As for why not come up with such a thing tar.zip? This is the year when the official zip software is shareware, not free software. So Linux is not directly or transplantation. That being rewritten, then there is no need to do the same and zip, gz after all, only a compression tube, do not bother packing.