Surely the devs focus on performance and scaling as well, if not at the level of managing servers? Having a dedicated ops team is a necessity, but it's important to keep developers in the loop on operations as well.
As the architect of the systems, I focus the designs on scalability and performance and the devs implement it. So, whether it's a dev or its an architect, someone has to be thinking about it. But having an ops background helps with knowing how to scale.
That's because we have a dedicated ops team who concentrate on performance and scaling, and leave the devs to write code instead of managing servers.