Just had a little thought on this situation, when WWE launched the Smackdown show, it was meant to be the WWF show on Network Television. Therefore, it would expand the audience to the people who don't have or don't want cable television.
Cable television does push the envelope a hell of a lot more than Network television, but the more family friendly product could entice newer younger audiences. With the younger audiences begging their parents to buy the upcoming pay-per-views, the merchandise and whatever else they can buy.
Look at it this way, when Smackdown returned to Network television in 2006. The opportunity to create new stars ensured. You had guys like Jeff Hardy, CM Punk, John Morrison who were floundering on RAW that were presented as the main guys for the show. Pair them up with established veterans like Undertaker, Big Show and Triple H, you have a very well balanced roster. Once the new fans see the newer rising stars (like CM Punk) interacting with the older well-known guys, the new viewers get the instant feeling that all these guys are stars.
With the network television, Smackdown was shown in a much bigger variety of homes. The CW had small local networks in different markets. So it doesn't matter if you had satellite, basic cable or even antenna, you had the chance to watch WWE Smackdown. Where the rising stars were shined just as much showcased as their older colleagues.
Smackdown might be considered as inferior to RAW nowadays, but when they were on network television, I believe they were mostly responsible for merchandise sales.
Feel free to give your thoughts.