Actually, if I'm not mistaken, most games are compressed in size by reducing the quality of the renders and animations or the bitrate of videos.
EDIT: I think this is the most used,
Cruncher
Yes, but that is by definition lossy compression. It can be applied to images and other media, but obviously not to code, nor to data structure (like a zip file)...
...BECAUSE what you get when you decompress it is not an exact copy of the original.
On this forum are marked as "compressed" all those archives which once extracted give something that is not the exact byte per byte copy of what you would have had if you extracted the zip published by the author.
If you want to make a "[LOSSLY] compressed" version of Harem Hotel you have to first unzip the official zip, crunch the images and other media, loosing quality, then create another zip that once unzipped will obviously give your smallest version of the game with lower image quality and not the version given by decompressing the original zip by Runey.
The split version is not marked as "compressed" because it doesn't contains lower quality media due to LOSSY compression.
It is indeed compressed, because they give Runey's zip as input to WinRAR which is a compression algorithm, but it is a LOSSLESS compression: what you get after extraction is an EXACT copy of what you have compressed, so it's not marked as "compressed" on this forum.
They simply compressed Runey's zip with WinRAR not to reduce it's size, but only to use the feature "divide in multiple archives of max 5 GB each".
The purpose is not to save transmission bandwidth, but to decrease the probability of connection timeout during download, because many users with poor internet connection (including me) experienced this problem even with JDownloader: 60% or so of download that can't be resumed and the only option was restarting from zero.
So once you extract the RAR you get exactly the same zip as Runey published.