Disable or reduce post revisions

Did you happen to see this note?

define( 'WP_POST_REVISIONS', 3 );

"Note: Some users could not get this to function until moving the command to the first line under the initial block comment in config.php. "

If you haven’t already tried it, try moving the location of the constant in wp-config.php and see if that makes any difference.

You may also have some success with a plugin solution, if that’s an option. http://wordpress.org/plugins/search.php?q=revisions+&sort=