It isn't that ridiclous it is true e-mail and mail exist as do telephones, but proximity plays a major role in contact. I imagine you have moved or graduated high school etc. If you went away to college or left your hometown for any reason there are a probably a number of people you intended to stay in contact with, but a week turned into a month turned into a year. I imagine that has happened to everyone out there and if you aren't able to keep in contact with friends how likely is it you will call, e-mail, your law school?
That is my point regarding these numbers overall law school graduates are people and upon graduation keeping your law school updated on your salary and job placement is not high on any lawyers priority list. You have family obligations, friends to contact, cases, bills, jury duty (just got that in the mail) , trips, basketball games, etc and going out of your way to update your law school on your employment status in very low on your priority list particularly if you live 100's of miles away.
I imagine you currently are not in law school so lets relate these stats to other items. There is a census that is released every 10 years did you contact them to make sure you were reported correctly, are you currently registered to vote in the City you live in? (you may or may not be) . Does your high school and college have your current address, phone number, have you reported your salary information to them? There endless things to report and frankly most people don't bother with any of it unless they have to.
When you graduate from law school there is no repercussion for not proving your employment information and most people simply either intend to fill out the survey (that was me it was on my desk to fill out when I passed the bar and I intended to fill it out, but a week turned into a year and five years later I never filled it out. Some people are very protective about their privacy and don't want to fill it out. Plenty of people do fill them out, but again every single law school graduate has their own personality and just knowing human nature I imagine people who live 500 miles away from their law school simply forget to send in updates.
If you or anyone else wants to take these numbers as gospel and an indicator of how a law school performs go for it people have had crazier thoughts, but I caution any OL or current law student to really use common sense when applying to law schools and not take these numbers to seriously as they are not indicator of how your career will turn out.
The truth is there are outstanding attorneys from every ABA law school as well terrible ones from every ABA law school. If you pass the bar you are licensed to practice law and what you do with that license will be far more up to you than the name of your law school.
At least in my anonymous internet poster opinion.