There are several reasons for this, but the primary one is that of all the network devices a site might employ, load balancers are typically the newest on the scene. Moreover, manufacturers are competing with each other at a feverish pace. They quickly release new feature-rich versions that aren't thoroughly tested. Another reason for the blame is that load balancers are not very well understood. A load balancer may not be malfunctioning, but if the people configuring the unit don't understand all of the features or troubleshooting techniques, they may unduly lay blame on the load balancer.
Load balancers are also in the direct path of all traffic to a particular Web site.
By looking at Figure 2 below, you can see that if the load balancer stops working, the entire site stops working. This is why a firewall is often a suspect, too, but to a lesser degree since it is generally a simpler device than load balancers. Considering these points, it's easy to understand why load balancers too often take the rap for a Web site's misfortunes. The problem, however, is that blame can lead to misdiagnosis of the real culprit and delay a remedy. MRTG is invaluable because it provides historical and graphical trending for network devices, whether they be a server, a router, or any other device with an Ethernet interface.