I can only tell you what happens where I work. You can get hired without the certification, but you make less money. However, once you are certified, you get an increase in your salary, automatically.

So, if you have been working at the company 5 years you now make a minimum on 63k (this is based on minimum starting salary +3% increase each year. If you impress you could make more). You are not yet certified, but are taking classes to get a degree. Now, John comes in. He is certified, but has no experience. He is automatically starting at around 60k and in 5 years will be earning 68k.

Then the company says to you "Hey, you are really good, you could make more money and if you get certified, why don't we send you to classes." You take the classes(they pay), you get certified, you get 5k more in your check and work more hours. You have your degree and now you are certified. If you quit and go to another company you could make about 10k more than the one you left.

I know this because it happens all the time here. And when people leave, they usually take a few others with them.