Hi Srinivasan,
Thanks for sharing your views. Actually I tried url without giving any parameters with both URL navigation and HTML preview port binding but unfortunately doesn't work out for me as well. Like I mentioned some websites do not allow to be displayed in frames this might be the reason for it I guess. Google maps are working fine as well.
So, can you plz. try to design a simple HTML mashup for any website in your system and share a screenshot for it? So that the problem can be found out.
Regards,
Saurabh