First of all ROS is a commercial software package and OpenWRT is a public software package. ROS can provide a lot of software that you can use and you do not install it. However OpenWRT you need to download and install the packages for your need. Please note some of them are not stable (or may be I am not good enough to master OpenWRT).
For ROS, there are many powerful hardware (called Routerboards) platforms on which ROS can run.