This is the question I've been hearing all too often these days: "We have a firewall, so my network's secure. Right?" or "You guys are monitoring my network, so it's secure. Right?"
Now, I won't get into too much detail here but let me just say there's a HUGE difference between managing a network vs. securing a network (ie: monitoring and maintaining a network for performance, stability, and up time vs. monitoring and securing it from the perspective of potential intrusion activity), two completely different purposes and, therefore, two completely different requirements, toolkits, and services delivered.
That said, I'd rather focus on the initial, essential question of "Is my network secure?"