It’s worth the quick read, but his core message is short, and to the point:
Over the years, magic items have become something that most players simply expect. In fact, in later editions of the game, characters were balanced with expected encounters assuming a certain level of magical gear. While that might be accurate, it raises a couple of problems.
First, treasure ends up being a part of the characters’ advancement track, not a reward.
Second, if magic items are assumed, they lose some of their mystery.
There’s a certain element of “well, duh” at work here, but it is important to note what Monte has recently come back to Wizards, reportedly to begin development of D&D 5e. I’m hoping this is an indication of what the developers are thinking about in terms of design philosophy for 5e, after 4e sucked a lot of the heart out of the game in favor of tight mechanical balance. At least in my opinion.