I thought so too, but then I made a little experiment:
pilif@shion:~$ curl -I -H "Host: example.com" http://198.252.206.16/
HTTP/1.1 404 Not Found
Content-Length: 4129
Date: Sat, 16 Mar 2013 12:28:22 GMT
vs.
pilif@shion:~$ curl -I -H "Host: example.com." http://198.252.206.16/
HTTP/1.1 400 Bad Request
Content-Length: 334
Content-Type: text/html; charset=us-ascii
Date: Sat, 16 Mar 2013 12:28:56 GMT
The IP is the one from stackoverflow.com. When querying for a host they are not configured (try any), you will get a 404 plus an explanation page that the selected Q&A community doesn't exist.
When you try the same host with a trailing dot, you get a generic IIS error 400.
This is too much of a coincidence and I value it as a strong sign that my hypothesis might be correct. I have no IIS at my disposal to replicate paulbeattie's experiment, but the outcome he described further helps confirming my suspicion (no matter the downvotes he got)
Same experiment works with microsoft.com too:
pilif@shion:~$ curl -I -H "Host: example.com." http://65.55.57.27/
HTTP/1.1 400 Bad Request
Content-Length: 334
Content-Type: text/html; charset=us-ascii
Server: Microsoft-HTTPAPI/2.0
Date: Sat, 16 Mar 2013 12:35:10 GMT
Connection: close
pilif@shion:~$ curl -I -H "Host: example.com" http://65.55.57.27/
HTTP/1.1 200 OK
Cache-Control: private
Content-Length: 0
Server: Microsoft-IIS/8.0
(snip)