There are at least four separate jobs that are often confused together because popular tools integrates them:
- Archiving: the ability to combine multiple files (including metadata) into a single file, preserving as much things as possible. In Linux/Unix world, archiving is traditionally done in TAR file format.
- Compression: the ability to losslessly minimize the size of a stream of binary data. In Linux/Unix world, this is traditionally done by GZip and BZip2.
- Encryption: the ability to scramble data with keys
- Checksum: the ability to detect (and possibly correct) errors.
The ubiquity of .tar.gz and .tar.bz corresponds to Unix philosophy of small tools doing a single job well, over a single tool that does everything. The TAR file format does not support compression or encryption, but it can be compressed further by any compressor (including as .tar.zip or .tar.7z). The job of GZip and BZip2 is simply to compress a file stream to another filestream, the compression layer does not need to care how to preserve metadata or encryption or checksum. Over time though, several shortcuts have been made in
tar program to work with a compressor more conveniently.
In zip and 7z file format, these separate jobs are done by a single program in a single super file format.
Why does the trend above appear to hold, even though all of these are portable formats? Are there any particular advantages to using a particular archive format on a particular platform?
Because it has been the way it's done, program source codes are traditionally distributed as .tar.gz or .tar.bz2, because preserving file permissions, modification time, etc are important for various tools used for programming (e.g. make).
The separate archival and compression step has worked for years very well, it has a clear advantage of being able to freely mix and match archival and compression, and its disadvantage (a 2-step compression process) can be easily circumvented by developing smarter tools (most modern linux compression program will directly compress to .tar.gz or .tar.bz2, hiding the intermediate step).
There is no strong reason to move to other file formats, newer compressors does not have a significantly better compression rate to justify breaking the tradition and tar can preserve everything well enough.