The associated graphic is some random “Maximum PC Magazine via Getty Images“ thing. You mean they have nobody that can take a photo of the inside of a PC?
Then the source of the article is not PCI-SIG itself but a TechReport article: https://techreport.com/news/32064/pcie-4-0-specification-fin... which, frankly, is much more packed with info and deets. In contrast to Engadget there's a nice info-graphic showing the evolution in bandwidth over the years _plus_ there's a table with PCI specs 1 through 5. Finally the source there is PCI-SIG itself: http://pcisig.com/ and from there you can root through the spec revisions: http://pcisig.com/specifications/review-zone – being as someone else pointed out here "PCI Express Base Specification Revision 4.0, Version 0.9" and "PCI Express Base Specification Revision 5.0, Version 0.3"
I mean I do like Engadget, I've been going there years, but sometimes I ask myself why I do. Their tech event live-blogs are pretty damn decent I guess but I wish their articles had more meat on them like ArsTechica or AnandTech or TechReport or …