The additional line is only necessary if you wanted your file to start with 4 nulls.
I am assuming AutoIt did this because Binary(0) is writing a long (4 byte number) with the value of 0.
A file that does not contain null space and you write the hex 54657374 (Test) is going to be treated as a text file because without your line that added nulls that is what it is.
So I have to ask again what were you expecting/wanting when you chose to write a binary file, and more importantly how were you planning on reading and using this data in your program?
@OP,
7ZA.exe is the standalone version of the 7zip download that only supports 7z, xz, ZIP, GZIP, BZIP2 and TAR formats natively.
So looking at this copied information about comic book formats from the wiki:
.cb7 → 7z
.cba → ACE
.cbr → RAR
.cbt → TAR
.cbz → ZIP
Of course 7za will fail on the cbr file you posted about.
There are dynamic link libraries (and command line binaries) available for extraction of these archive formats available on the web, should you wish to automate the process or write your own application.
There are even some pdf user defined functions and examples on this forum if you search.
Regarding extraction:
The simplest method is merely to automate command-line applications for the various formats, a good example of a tool that does this is universal extractor;
http://legroom.net/software/uniextract
Whose AutoIt sourcecode (available at the site) might assist you; should you decide upon this method for your tool.
Mobius's post in Write Binary Data was marked as the answer