Marriage is a societal institution that's been around for ages. Its purpose is to be a component in regulating relationships between men and women. In Islam, it's just a legal contract that outlines the responsibilities the people in the relationship have to one another plus a few other bits. That said, I don't think it would be much of a stretch to say that's what marriage for all faiths is supposed to be like.

Is there a benefit to getting married? I think they question should be, "Is there a benefit to getting married in this day and age?"

Well in the Western world not really. You can have the discussions like ones above about tax benefits etc but I don't think one of these arguments really outweighs the other. Since cohabiting without being married is an accepted norm there is no need for marriage.

It is interesting though how, in the UK anyway, there are some bits of legislation that were (maybe are, I'm not sure) being discussed as to how unmarried couples should have things such as inheritence rights and the custody of children defined under law.

Kind of ironic in my opinion that people are even considering regulating unmarried relationships after rebelling against the concept of marriage. You already have the concept of pre nuptials. Seems to be that people have simply changed religions.... That which we call a rose would by any other name still smell as sweet?