Just because these benefits are often described as "intangible," it doesn't mean they are any less important than "tangible" benefits. In fact, these intangibles are often what make the tangibles--such as on budget and on schedule--possible.
What was surprising, however, was that many companies in the study--probably even ones that have been investing in project management for long periods of time--don't track their ROI. Why not? It's not as if this is some small investment or time commitment. If an organization was investing in the latest piece of technology that promised to save money or reduce the time spent working on a single task wouldn't they track that? Wouldn't they want to know they invested wisely?