Why should it keep these sockets? 
Why should it remove these directories? 
 

It should not remove that socket because Xvnc still running and accepts
connections on it.
It should remove that directories because kdm creates new random dir every time
he starts and dont use previous dirs.

1. stmpclean removes old sockets only.  Unless /tmp is mounted with "noatime" option, access 
time of the socket is updated each time new client is connected. 
 
2. According to stmpclean(8), 
"The stmpclean utility never removes files or directories owned by root. 
It is a feature, not a bug." 
 
I think that kdm should create its tmp directories in more appropriate place, so they could be 
removed by /etc/rc.d/scripts/cleanup. 
 

> I think that kdm should create its tmp directories 
> in more appropriate place, so they could be  
>  removed by /etc/rc.d/scripts/cleanup. 
Ok. 
/tmp/kde-kdm-XXXXXX 

$ mkdir /tmp/a
$ mksock /tmp/a/uuu
$ touch /tmp/a/ggg
$ sleep 10
$ stmpclean -v -t 0s
stmpclean[7823]: removed file /tmp/a/ggg
$ ls -la /tmp/a
итого 8
drwxr-xr-x  2 voins voins 4096 Июн 10 15:21 .
drwxrwxrwt  7 root  root  4096 Июн 10 15:20 ..
srwxr-xr-x  1 voins voins    0 Июн 10 15:20 uuu

отсюда вывод: stmpclean не удаляет сокеты, что подтверждается чтением
исходников.