The workings of the human body don't change from month to month or year to year. The understanding of it does (MRI alone has made huge differences, and PET scans and such), but there are basics, like setting bones and pulling bad teeth, that have been true for millennia.
Law is slow to change as well.
It's easier to regulate when you can have a standard in place for long enough that the students learning it in school will still use it when they graduate.
If you studied medicine, law, engineering, accounting, etc., in the 1970s, you're probably still able to do a decent job as a family doctor, a lawyer, a civil engineer, or an accountant. If you studied computers in the 1970s, you have just about zero skills from that time that are still applicable.
If you studied medicine in the late 90s, you definitely still have skills that are applicable. But you probably wouldn't be familiar with XML Web services, definitely wouldn't be familiar with Ruby on Rails, DotNetNuke, etc.
The thing about working in IT is that much of the production is closely related to research. Using a new technology to do a new thing, or to do an old thing better than before, is what IT is all about.
If you check, the people doing medical research are often not MDs. The people researching new materials to build buildings and bridges are not construction engineers. And so on. IT has the two subjects, research and practice, too closely tied together to truly standardize.
On the trust issue: Would you trust a doctor who got his MD from Harvard in the 60s, who reads the medical news, but who hasn't the foggiest idea how to operate an MRI or PET scan, who's been practicing family medicine solidly since then? For a regular MD type issue, yearly checkup, kid's got the flu type things, you would do well to trust that doctor.
Would you trust a computer programmer whose training was in the 60s, who still uses punch-cards, who hasn't the foggiest notion what an object is and thinks that database programmers are talking about second movies (which are never as good as the first one, except for Empire Strikes Back of course)? Would you hand him a project? Definitely not.
The same can be said for lawyers, accountants, civil engineers, etc., as for the family doctor.
So, self-trained or formally trained, it's the skills held and the familiarity with them, not the piece of paper, in IT.