For e.g. Firefox; when mounting their dmg file, the installer window is opened directly, without the need to click the mounted volume on the desktop. This is not the case for ThinLinc, where the iso is mounted and the installer window then has to be opened manually.
This difference was thought to be due to the different file formats of iso and dmg, but when using a custom dmg file it behaves like ThinLinc. There is something else than the file format used when deciding the automatic opening of the installer window.
The program DropDMG might be able to help solve this. I did not test if an iso were able to do this, but the generated dmg files opened automatically. Note that the program is proprietary with a 30 day trial.
Also note that the generated dmg file has the same background issues as mentioned in bug 5204 comment 5.
An iso built with the DS_Store taken from the dmg file generated by DropDMG does _not_ open automatically even if the dmg file does.
Either DS_Store does not contain information about if the installer window should be opened automatically, or iso:s simply can't be opened automatically.