The way I see it, eliminating a few digits of the serial number takes all of 5 seconds, and will hurt absolutely nothing. While it may have never happened, anything is possible, so not doing it could have a downside, even if the odds of it even being attempted are 1 billion to 1. Why even risk it over 5 seconds worth of your time to edit, or not types the full s/n?
Some criminals are very good at what they do, and can be pretty ingenious, so its possible one could figure out a way to use the s/n to get your gun. even if they failed in the attempt, and went to prison, your gun will probly still get tied up for a while as the cops sort it out, then as evidence for the persons trila for the attempt. Either way, you lose your gun for a bit, and I would rather that not happen, personally.
Also, as said, a vindictive person could use it just to get your gun tied up with the cops while it gets sorted out. Will they get busted for doing it? VERY,VERY likely, but some people are dumb enough not to realize that, and some just may not care, and 1 might just get lucky and get away with it.
Too many starnge, and seemingly impossible things happen all the time to say it's impossible, and minimizing the risk ven more takes a few seconds, so....
That said, I dont block out s/n's in my pics, but only because I have never had one be even remotely visible in a pic I took, so it wsnt nessecary. Just dont take a close up of the area whee the s/n is, and you dont have to do anything, and still get the benifit of not displaying it.