It might be that you have used blackhat techniques on the site or used blackhat techniques in building backlinks.
Yes, that's what I am talking about. Any thought on why this will happens? Is it due to the same whois information? Can I ask Google for the reason too?
Google algorithm changes on a regular bases. If you have a whitehat site, nothing to worry about. If not, then just use the newer blackhat techniques on a new domain.
Not really just few of my sites were penalized by Google... There are times that I could not really figure out the reason of penalizing the sites..
One of my examples is "www.isefriends.org" and it was still indexed in last week but happened to get de-indexed in the past few days.