KRIONI Those file size are typical. A standard read-only disk image created by Disk Utility is about 10 MB, even when the application and README are less than a megabyte combined. However, the developer could make a Compressed Read-Only disk image, which would then make the disk image about the same size as zipping that 10 MB standard disk image, and, unless their web server cannot serve DMG files directly (doesn't know the MIME type so web browsers try to load it as text and see gobbledy-gook instead of downloading the file), make zipping the disk image unnecessary.
Strangely, many developers don't know about Compressed Read-Only disk images.
(Version 0.4.1)