] ...I think the less wealthy people generally had more children back then so someone could help support the family either in trade or on a farm.

This touches on an important aspect to consider. From studying man and man's behavior, we realize poorer people, on average, have more children than wealthy people.

CherylS mentioned income as a reason. She hits the proverbial nail on the head. The reason is purely economical. The wealthier you become, the more of a defecit child rearing becomes. For example, the typical modern, upper middle class family is much more likely to accomodate a child's need for education because it is in their financial power to do so. Most children born from this social class (and higher) are expected to go to college and pursue higher learning, and their parents are expected to provide for them. Just having sent one, two, or three children amounts to a huge expense. On top of that, we buy our teenagers cars, get them credit cards, buy them computers, etc. In our modern day society where the average parent is wealthier than many people in other countries, children are a financial drain. (This doesn't mean, of course, that we don't love them, but that's just how our society is set up.)

However, in other social classes, other countries, and other societies, children are still a financial assett. They provide an extra pair of hands to help work and are another source of income. Some families, for example, live as one extended family under one roof where they all pool together their incomes to help support each other. More children would mean more income for the family further down the line. In this case, they don't buy their children new clothes every year, buy them cars once they turn 16, get them computers, buy them video games, etc. In such instances, children are a financial assett, not a financial drain.

But regarding the original question, we must remember that there were other social circumstances. In Regency England, we all know it was important to bear a son to inherit the family estate. In P&P, for example, the Darcys already had a son, and Mr. Bennet even says that he and Mrs. Bennet kept trying to father a son, but instead wound up with five daughters in their attempts. Also, wealthy men were away from their families much more often than not-so-wealthy husbands. Wealthy men had their land and tenants to oversee, business affairs to overlook, and they had the financial means to fund their extensive travel, be it for work or for pleasure.

We must also remember that in that time marriage was more of a contract between two families. Few women had the liberty to choose a mate for love, because social pressure and family pressure spoke against it (unless it was already a suitable match). This is even more true for members of the aristocracy, where marriage was more an alliance than anything else. If one party had the name and the other party had the money, they'd both benefit from such an alliance. Love was rarely a consideration for members of the aristocracy (which is why Lady Catherine was so against Darcy marrying Elizabeth). Marriage was more "political maneuver" than "loving relationship" for the rich and the nobility. If such a union occurred and there was no love between the two parties, it would hardly be expected that they would produce more heirs than they needed. The middle class and the poor had much better chances to marry for love than a noblewoman or a daughter of a wealthy man did, and those unions would most likely produce more offspring.