Some people don't like to reveal the entire serial number for security reasons. The usual explanation is that someone sees the whole number and claims that it belongs to them and was stolen. In the 15+ years that I've been active on the Internet, the legitimate times this has happened (and been verified) I could put on the fingers of one hand (and have several fingers left over).
I've listed the whole serial number on every firearms I've posted pictures for an equal time and have never had a problem.