The people that normally write those articles do it, usually, from a company perspective, actually forgetting to highlight the employee perspective on this matter.
As an employee, I can assure that this is a completely accurate sentence. As a person, I have experienced good and bad employers and different policies and approaches to the theme of "employee happiness vs productivity".
And from my perspective, sometimes a company does not need to spend thousands in fancy rewards to make an employee happy and as a consequence, more productive.
Most of the time - in my own view from past and current experiences - the fact that an employee feels that there is someone to turn to if an issue is raised, is half way to the goal.
And please, do not mistake yourself by saying "That's why companies have HR departments and supervisors".
Sometimes, we don't feel comfortable with the people that are supposed to be our "help-on-reach", as they have little or no knowledge of they real job requirements and just go-with-the-flow, sometimes minimizing certain aspects that should be seriously relevant for them in the interaction with co-workers.
In fact, - and again based on my own personal experience - those are the people that can help to make things worst, either being or not conscientiously.
Another thing to be aware of is the fact that some people are normally so delighted when they receive a job offer that it is important to review and in some cases to renegotiate certain aspects of the offer. It's better to do this from start, instead of going with the idea that "after I get the job I can worry about the things that I disagree with".
A contract is a legal agreement between parts, meaning that there are certain terms and conditions that are going to be applicable for the duration of it, some of them that people won't have the possibility of negotiate/ change when already on the job.
What I mean by this is that the fault for unhappiness at work is not always
Happiness is not only needed for personal life. Love what you do, seek ways to improve your job and your daily tasks. Things will turnout better and people will notice as well that a Happy employee is a productive one