Accessibility aspects of Close buttons on dialogs?

[Christian Rose <menthos menthos com>]

As those of you who are following the usability list might already know,
"Close" buttons on dialogs are being discussed. It is debated whether
dialogs that don't have any other buttons (like instant-apply preference
dialogs) should have a GTK+ button labeled "Close" at the bottom to
dismiss the dialog, or if the window manager provided window close
button (usually a cross) at the top of the window is enough.

I myself beleive that a "Close" button at the bottom of the dialog would
among other things be a help for accessibility, since it helps keyboard
navigation: A window manager "window close" shortcut doesn't have to be
used or remembered, and the dialog will always be closable whatever the
window manager happens to be.
Am I right or wrong in my assumptions? What are your opinions regarding
the accessibility of either alternatives? What would you recommend?


Christian