I think the most interesting thing is the the last graph - "Market Share for Top Servers Across the Million Busiest Sites". Apache has held steady over the past 3 years, yet the decline of IIS is mirrored by the growth of nginx.
I know a few shops where IIS servers were hidden behind an nginx layer, which would agree with your statement - but does not necessarily mean that IIS is no longer used, just not publicly visible.
This is exactly right. There is a great scenario for using nginx out in front of any number of workhorse app servers.
Interesting - I didn't know that those worlds mixed. :) BTW, I wasn't trying to imply that nginx was directly replacing IIS. I interpreted it to mean that sites running nginx are breaking into the top million at a faster rate and sites running IIS are dropping out at a faster rate.