Some brands keep the same logo for decades, but some like to reinvent the wheel every once in a while. It's amazing to see the transformations that some logos have taken as the years pass and design grows. Sure, there is risk involved, but if it keeps the brand fresh without offending brand loyal customers, I'm all for it. Some of the biggest names in branding have done it a lot...probably more than you are or I am aware of. And that's a good sign that they did it right with little disruption.
Pepsi is by far my favorite evolution. It came a long way, and ironically started out looking very much like Coke.