Yes, that's basically how the 'create account' on the admin side goes.
You must remember that this script started as a personal one-off, never intended for release, just to add the ability for users to signup an account and retrieve lost passwords.
The admin panel was latter added after requests. The create account was added to the admin panel after a request.
While I agree with you that the ability of users to change their password from within RoundCube would be very welcome it is not what this addon was started for.
There is also a addon already available for this feature (adding change password to RoundCube), however I have not had the chance to test this out myself yet.
As long as this addon works, why recreate the wheel ?
If someone has tested this password change addon and can verify whether it works it would be helpful.
If it appears that it doesn't work then I will certainly add a user password change feature to the next release.