Some of it depends on the nature of the URI though. The article is about linked resources, but a lot of URI usage isn't really about linked resources. Many of these can change reasonably.

For example, is there any harm in changing where that contact us form points to? Do you have to maintain the contact us forms API to be backwards compatible forever? This really depends on what you are doing.

I agree with the article as it relates to documents for the most part. There are cases where maintaining URL backwards compatibility is a problem due to unforeseen dead ends. However, for the most part it shouldn't be. However, URIs needs for persistence varies so widely that I don't know one can generalize much beyond that.