When you request google.com, google responds with this:
HTTP/1.0 301 Moved Permanently
Location:
http://www.google.com/
They are simply detecting the URL
http://google.com and forcibly redirecting you. This is not a function of DNS.
You could configure IIS to do this. Create a web site with the host header of "abc.com". This web site would simply be a redirector to
www.abc.com.
Alternatively you could do the same URL check somewhere in code and then just redirect the client.
-Peter