Nice article, whose central message ("don't bundle your tools") is widely applicable to domains other than monitoring. Small, specialized tools that can be combined together is the very essence of the Unix philosophy.
The problem is particularly acute in monitoring because you tend to need to monitor many disparate systems and subsystems in a very fine-grained manner. It needs to be reliable and not impact performance no matter where it is run which usually has to be everywhere. The Unix philosophy is definitely useful on a wider basis, but monitoring could be the poster child.