It's not for the compression, Shikaku, it's to have your comics organized neatly with one file per issue.
Yep, also a displayer like CDisplay will allow you to browse the covers
in a directory full of zipped issues, to choose the issue you want to read.
It will also allow you to navigate per issue (archive), and most importantly
set your viewing prefs for all the images as you read.
I can theoretically read the comics image by image with the
built-in jpeg viewer, but each time it loads the image it resizes it.
So you have to zoom in again manually per page. Which is a pain
when all you need to do is orientate and zoom to a level that you
can read the speech bubbles.
If I ever learn to code for the gp2x, in theory a lot of the features needed
may already exist in SDL libs. eg display picture, open zip/rar ?
And it's just a case of enhancing the functionality of the current photoviewer
with some save state/prefs.