I both agree and disagree with this. They do need to have a range of games, both for the entry level gamers and the experienced ones. I don't think there is a doubt where SC4 falls in its appeal. I really have no problem with the direction they are taking Societies, because they want to appeal to the newer players who may in turn look into the games that came before it. In my eyes, SC:S isn't a sequel, its a spinoff. I personally don't think it sounds interesting, and don't plan on playing it, just like with many other games that are produced.
I don't really doubt that at some point in time, SC5 will come around. They want to appeal to new gamers first, since the majority of the SC fanbase is older. When we get a true sequel, they want the newer people to the series (those that have only played the Sims and Societies) to be able to play a game alongside the longterm fans like the majority of people here.