I can't believe... I tested it here and you are right. I always tought that you needed permissions to the file to delete it. I think it is a big security problem anyway...

bash-2.05b$ mkdir test
bash-2.05b$ cd test
bash-2.05b$ ls -la
total 12
drwxr-xr-x    2 dcid     devteam      4096 Aug  3 08:57 .
drwxr-xr-x   65 dcid     devteam      8192 Aug  3 08:57 ..
bash-2.05b$ sudo touch file1
bash-2.05b$ ls -la
total 12
drwxr-xr-x    2 dcid     devteam      4096 Aug  3 08:58 .
drwxr-xr-x   65 dcid     devteam      8192 Aug  3 08:57 ..
-rw-r--r--    1 root     root            0 Aug  3 08:58 file1
bash-2.05b$ rm file1
rm: remove write-protected regular empty file `file1'? y
bash-2.05b$ ls
bash-2.05b$ ls -la
total 12
drwxr-xr-x    2 dcid     devteam      4096 Aug  3 08:58 .
drwxr-xr-x   65 dcid     devteam      8192 Aug  3 08:57 ..
bash-2.05b$ sudo mkdir dir1
bash-2.05b$ ls -la
total 16
drwxr-xr-x    3 dcid     devteam      4096 Aug  3 08:59 .
drwxr-xr-x   65 dcid     devteam      8192 Aug  3 08:57 ..
drwxr-xr-x    2 root     root         4096 Aug  3 08:59 dir1
bash-2.05b$ rmdir dir1
bash-2.05b$ ls
bash-2.05b$ ls -la
total 12
drwxr-xr-x    2 dcid     devteam      4096 Aug  3 08:59 .
drwxr-xr-x   65 dcid     devteam      8192 Aug  3 08:57 ..
[download]

*hum... this is why we need the sticky bit in the "tmp" dir.. I completely forgot about it.