Back when I was in high school and college in the late 70s through the mid 80s, I ran lots of road races. It was always made abundantly clear to me that it was my responsibility to make sure my bib was showing and that the race personnel located out on the course writing down numbers registered that I passed by that point. I ran races sure I'd be disqualified if my bib was not showing. In 1981, when I was even more scatterbrained than I am now, I drove from Indiana to Missouri and ran the St. Louis Marathon as a senior in HS with a bunch of college friends. We stayed at the tall sponsor hotel a block from the start. As we were walking to the start line 10 minutes before the race, one of my friends asked me where my number was, and I realized it was still on the hotel room bed. So I ran up a huge number of stairs to get my number, worried (stupidly) that the elevator would take too long and even more worried that if I didn't have my number I'd get DQ'd. Needless to say, the race was rough.
These days, there are lots of excellent "race rules" in the packets and on-line information for each race, but in my conversations with race directors, they are unwilling to use their right to DQ a runner when they violate the straightforward and simple rules. One RD told me he was afraid of legal repurcussions (I think this excuse was lame), while another told me that he hoped the threat of repurcussions would reduce cheating and other problems. Still another told me it was way too much work to comb through the controls for each runner. Several marathon RDs told me that they suspected wideapread cheating for Boston qualifying times, but I don't think anyone has really quantified the problem in a meaningful way.
The bottom line is that Litton could have been DQ'd from every single 2010 marathon, in my opinion, because he broke the simple rule of not having his number show clearly. I got called on that once in a small-town race in Anaconda, Montana when I wore a windbreaker over my number in nasty weather. I was kind of pissed about it, but I also realized that it was my bad.