If you define the Web instead as "stuff that happens in web browsers" then... you come to the same conclusion. What definition of the Web would not include all this video traffic?
I could see someone being interested in subsets, but yeah, they don't have a definition here. One that might be interesting is: what amount of time do people spend reading mainly textual documents online? That'd correspond somewhat to a classical view of the web as hypertext (you know, a "web" of interlinked documents).
That would, though, have to exclude not only watching videos, but also paying your credit-card bill on a bank's website, and other such web-as-thin-client rather than web-as-documents uses. Forums like this also occupy a weird place, since they're somewhat more like web-as-listserv/usenet-replacement than web-as-documents.
But, I'm not sure the end result would actually show a decline anyway. Wikipedia and blogs, for example, are more or less hypertext documents in the old sense of the term, just with some new conventions for organizing and editing them. Wikipedia alone probably rivals (exceeds?) the entire mid-1990s internet in size and readership.
