First, I agree that learning your computer skills by just DOING things is better than most college courses and cert courses. But in line with the excellent post by Galaxiom, particularly his first paragraph, I can tell you with absolute certainty that the trend towards external certifications is due to the incredible complexity of today's modern business world.
Modern managers simply have no way to evaluate people for all of the jobs that might occur in their company. Even within computer science fields we have specialties such as networking, database administration, system programming and administration, device driver programming, applications programming, compilers, security, ... Every one of those can probably be further subdivided at least a little bit.
Heck, my first "real" job led me to quickly become the HR liaison for computer programmers. I would screen the resume' for applicability and potential. We were always looking for people but often got people scurrying out of the woodwork. (Sounds harsh, but trust me, some of those applications were horror stories!) I helped the HR people set up lists of folks to call (and the order in which to call them) to determine whether the persons were even worth the price of an interview trip.
The problem these days is that there are SO many specialties that an HR department would need to hire someone from each specialty to evaluate the persons. The use of external "standard" certifications is the "cheat code" that lets the HR department make an educated guess that the person might be at least worth a look. It still doesn't say whether the person can program their way out of a paper sack, but it tends to indicate that when their eyes glaze over, it isn't because of the concepts covered in the certification.
I got my first real job thanks to a guy who knew me from college and had seen some of my work. He knew I could code efficiently and also knew that I understood device control issues. So I got my foot in the door as a device-driver guy. But my major wasn't computer science. Nor my minor. I had only taken two computer science courses. The rest was "learn by doing successfully." That is where my operating system and compiler and other odd tid-bits of knowledge originated.