THIS IS INTENTIONAL on the part of Magento. They want a high fail rate. It ensures that only orgs with lots of money (who can afford a couple failures) will get a large number of certs and become official Magento partners, and since you pay for each test more failures means more money.
They have carefully structured the cert so that about 1/2 the questions are actual general skills and useful knowledge for working with the framework and about 1/2 are rote memorization such as, "What is the EXACT class name and Method Name that does X?" where options are
My_Basic_Class_Car::doThing() My_Basics_For_Class_Car::doThings() My_Class_For_Car::doThing() My_Class_for_Cars::doThings()
You need like 75% to pass... so if you're really lucky you can guess your way through the memorization portion but 90% won't pass on their first try.
If I were a hiring manager looking at a candidate with a Magento cert I could glean 1 of 2 things:
1) This person took the cert independently and cared enough to cheat or pay a lot of money to get it.
2) This person worked at an org with enough institutional knowledge of Magento and their payola process that they probably learned SOMETHING while they were there.
2) There are several parts to the exam but none of them involve an evaluation of how you write code, its all multiple choice.
3) The cert itself and studying for it doesn't prepare you for actually building a Magento site in any way. The Magento certification program is really just a way for businesses to get access to "leads" and get free advertising from Magento. Having more certs just helps a company look good.
4) If your buddy is experiencing a lot turnover my experience of the eCommerce industry and Magento shops specifically is that they are more inclined to put a heavy emphasis on "culture fit" and be high stress environments. They say, "If you see assholes everywhere, maybe you should look in mirror..." but it might just be your friend is experiencing the reality that eCommerce development is NOT the same environment as the Wordpress chop shops he may have started in.
Last year I worked with a certified LPIC-3 system administrator and deploying a trivial wordpress website at AWS took him 1 week. He was fired 1 month later. His CV is very impressive with lots of certification badges (I checked the codes of several badges and he is really certified).
From the second paragraph down, you're absolutely right for non-software companies. They still don't have an understanding of how to build software development into their business model. They don't realize that the low barrier entry to building software does not mean it is a low-cost, low-risk endeavor, nor do they understand how to extract value from a completed software project. They go straight from "Bob the executive has a cool idea," to, "Let's hire 3 full-time devs."