Almost every doctor or lawyer I know would likely gladly trade CE for "programmer-style" self study - and CEUs can keep your skills sharp if you do them right.
They can, and are supposed to, but they have morphed into a box-checking exercise used to keep politicians and professional guilds happy and management asses covered. Hence the reason most of these professionals see the requirement as a burden. I felt the same way back when I was actually working as an electrical engineer.
That said, self-study is a different animal from the side project nonsense that the thread root is referring to. I personally engage in a significant amount of self-study. Some of it a roll back into my day job, some I experiment with in my free time, the rest is purely academic knowledge acquisition. I don't have anything tangible to show off, though, because most everything I have done off hours is the software equivalent of a carver or welder practicing with scraps.
Maybe that isn't the right attitude for a programmer, but in that case a programmer is a different animal than any of the professions listed previously.
- Medical professionals require 48 hours of continuing education per two years, of which 24 may be informal self study or hospital lectures - Legal professionals require 15 hours of continuing education per year - Professional engineers require 17 hours of continuing education per year
CEUs are obtained either through classroom instruction or attendance at recognized conferences or seminars. This is not the same as doing your day job after hours for fun or because you feel you must in order to actually get a new job. It certainly does not keep your skills sharp.
Doctors, lawyers, and PEs also have professional societies and often employers to facilitate obtaining CEUs in the most efficient manner.