We support both Networker & Commvault with many many support customers, and basically when asked what the difference is between them, its easy...
Networker is an Enterprise solution, Commvault isn't....
Commvault may one day become a backup solution that can support Enterprise Environments, but until then thats basically the answer.
do a search for v7.3 and you will see just how may headaches are out there in backup land.....v7.2.2 is a good workhorse and is still my preference...