The problem I see with the graph is it's based on percentage of total traffic but it doesn't take into account a huge increase in bandwidth and internet users. Put it in perspective and you realize the web's "peak" according to this graph was when most people were using 56k modems (2000 which was about a year after V.90 modems started hitting the street).
There's also an efficiency factor. Ajax type technologies have dramatically shrunk the size of the data chunks being passed back and forth. Back in 2000 most were still resending the whole page on every refresh.