Differences of the nature mentioned here lead to arguments? Not always! I have had some of the most enriching and fruitful relationships with people with whom I had very little in common. Howerver, the one aspect mentioned by Kaiser is most pertinent- value system. It is definitely the platform which serves as a base for building any future relationship.

I have examples in personal and social life where very different and far removed individuals have come together in marriage and have ended up with very successful ones too.

In any meaningful, reliable, durable and sustainable relationship of any nature, from the one end of the spectrum of personal relationships to the other end of biz/formal relationships, values and especially core values have to be shared/similar/common. Other differences do add to the experience and the taste of life during the course of an association.

people want peace from life, not an endless round or arguments

Rightly put !! But when you talk of psychological propensity to look for similarities, i would like to add that differences act as better brain stimulants and without a spur of that nature life would seem trite.
It is common ofcourse and thats the reason I raised the question. So you mean to say that we believe in something and practice something else? If so, arent we all living a life of double or maybe triple standards?