Stay in an unhappy marriage for your kids?

According to a survey by a parent magazine, only 20% of American parents will keep themselves in an unhappy marriage just for kids' sake. 
As far as I can imagine, this number may at least double in China. 
Two reasons: One is the culture of 100 percent devoted love to (biological) children, and the other is the shortage of love for non-biological children.
There is a old saying in China: "Even a vicious tiger will not eat its cubs" or "No one is capable of hurting his own children".  As a culture, most Chinese put kids in the first place in their lives above anything else: work, marriage, personal hobbies.  One of the reasons, is that in Old China, when people got old and could not work, the kids are the only resource they can seek to for food and shelter.  Situations have changed a lot since the retirement, medical care, social security system develop much better in recent years.  However, the culture has not changed much.  Most people devote all their love to the kids, no matte what.  Almost all the parents believe that giving their children a complete home with both of the biological father and mother present is the most important thing to guarantee a healthy psychological and physical development of their children.
At the same time, in most circumstances parents treat kids completely differently depending on whether there is a blood relationship. Usually when people talk about abuse cases, the first question being asked will always be: Is the child biologically related to the mother/father?  Because most stepparents will not care much about their stepchildren, when couples are in bad relationship, the fear of getting a stepmother/stepfather for their children usually prevents them from stepping forward to divorce - the fear of getting their kids into a bad situation is big enough to prevent people end their unhappy marriages. (Having said that, it always surprises me that both situations seem not uncommon in US: Step parents in US get along with their step children while biological parents abuse/kill their kids - both of which are rare in China).
Therefore, usually in China, couples will try their best to avoid divorce if they have kids: they choose to ignore affairs, abuses, lack of love, you name it.  The reason is simple: people believe that the love from biological parents is not substitutable by ANYTHING ELSE.
Now the question is: Will the children suffer more from an unhappy married biological parents or a happy married mom/dad with a stepparent without too much love.
The answer will never be the same in different culture and to different couples.