It's not really much more open. Similar to some other network hardware (e.g extreme networks) it runs linux for the management interface. The switching/routing ASICs that does the actual work are still proprietary. It allows for a bit more flexibility in that it supports apt, but IMHO an image-based update system is preferable on network hardware, as you are not vulnerable to apt-breakage or anything like that. You know, whatever happens it will boot, always.