I can understand when something isn't selling, a company needs to do something differently. But I find it very difficult to believe that the 527, one of the most popular of their line, wasn't selling. When they discontinued the 550 there was at least some amount of honesty, that they were trying to reduce production costs. With all that being said, the end of the 550/557/527 and the introduction of the 600 series can only amount to two things 1. an effort to further reduce production costs and 2. making changes simply for the sake of making changes.
Because there are always people who like buying something that is "new", they will probably sell well for a time. After the new wears off, I seriously doubt the new rifles will be outselling the older models.
I don't know why it is that so many things which never needed replacement, get replaced for something that is allegedly "better", even when people clearly aren't happy about it....(think of new formula Coke and what a disaster that was, among others) But customer satisfaction is the absolute last thing that drives such activity. My 2 cents, based on many years of observation on a variety of products.