By default, KWallet asks for the password each time it is opened. Thus, I first enter my login password, then the KWallet password when using KDE. In contrast, the gnome-keyring uses the login password so users have to enter only one password. Can KWallet be configured so that it uses the login password or at least doesn't ask for a password each time the wallet is opened?

The former had been reported as a feature request on bugs.kde.org in 2004. Any progress since?

As far as I know, there has been no changes in regards to being able to use the same password as you login with.
However, you can set no password, which will allow it to be opened immediately.

You can change the password on an existing wallet using KWalletManager. This can usually be found in the hidden icons section of the System Tray. Simply right click on your existing wallet, and select Change Password, then provide no password and confirm.