http://www.dribin.org/dave/blog/archives/2006/01/16/keychain...
https://developer.apple.com/library/mac/#documentation/Secur...
Gnome keyring definitely uses encryption to store passwords; they take security pretty seriously: https://live.gnome.org/GnomeKeyring/SecurityPhilosophy
As opposed to what? They need to have access to the plaintext passwords somewhere; it's just encrypted when it's stored on disk.
> Shocked as well, not to mention seahorse is launched without asking my password.
The default keychain uses your login password, and it's unlocked at login. This is easy to change if you want to have to unlock it every time you use it.
Many programs that require passwords (e.g., mutt, offlineimap, msmtp) let you specify a command to retrieve the password, which is really easy using pass.