Ted Kesik, Professor of Building Science and author of the report, raises the issue of the expected lifetime performance of the glass (5-15 years, or 15-25 years more conservatively) and the costs of eventual replacement on a massive scale.
Kesik's report makes one thing clear: many sealed units fail. And with that failure, most of the R-value ceases to function. Factor in manufacturing, transporting, and installing replacements and the question of thermal resistance becomes one part of a complex assessment of costs and environmental considerations. In older buildings there are also aesthetic concerns with existing glass.
Kesik also talks about alternative methods of construction to glass walls such as punched windows and the use of materials like brick and masonry block.
It's difficult to say what conclusions can be drawn from the report for Vancouver, where the climate is milder but glass towers are plentiful.
On a related topic, ouno blog recently posted on the questionable viability of skyscrapers as a building typology.
Kesik ends his report with this:
"Today's glass condo towers are not as energy efficient and far less durable than their 1960's counterparts. Is there any industry where 50 years later, the products it produces cost more and perform worse than their predecessors?"