Disable WYSIWYG editor only when creating a page

The best way to do this is by adding ‘user_can_richedit’ filter, like so:

add_filter( 'user_can_richedit', 'patrick_user_can_richedit');

function patrick_user_can_richedit($c) {
    global $post_type;

    if ('page' == $post_type)
        return false;
    return $c;
}

Hope it’s useful 😉