a) That growth is outpacing internet traffic growth, and has for many years now. Internet traffic CAGR is 23%[1]
b) The shift from desktop to mobile should have the effect of reducing clicks.
c) Since some of the growth is video, I would expect a decrease in click growth related to this as well. Video adds to bandwidth growth pretty directly. Click growth would be less direct.
Sergey and Larry, at least at one time, might have expressed concern:
"The goals of the advertising business model do not always correspond to providing quality search to users"[2]
[1] http://www.cisco.com/c/en/us/solutions/collateral/service-pr...