I believe you are misinterpreting the graphs. The top two graphs are indicating how many domains run on each type of server. Apache is certainly doing very well here... around 32 million domains run on Apache servers, with increases like you described.
Near the bottom however, we have a different story told. Down there is the number of SERVERS installed. At the top is, of course, Apache with about 15 million active servers. However, when you look at the marketshare changes for active servers, it's completely flat.
What is happening is that Apache servers are running MORE WEBSITES per server. In other words, the big website providers, that host 5-500 websites on a single box, are running Apache. Those big companies are getting a lot more subscribers, in leaps and bounds, as hosting prices drop dramatically. Everyone and their mother are getting a website, but not on their own server... on a big hosting farm, which runs Apache.
Of course, more servers are coming out... but the market share, server per server, is barely changing, as the last graph shows. In the last year, IIS installations rose from about 4 million to about 5 million. In that same period, Apache went from about 11 million to 15 million.
BOTH servers rose about 25% over the past year, so the market share barely changed. But Apache servers are hosting many more websites per server... Apache tends to be run by ISPs and hosting companies, because it is much better at running for colocated users, who can administer their site with a shell account and via the great web management packages written for Apache. IIS tends to be used by companies running their own server, which means fewer domains per server.
So while Apache's domain count rises meteorically, the installed server base is rising on par with IIS.
I'd like to stress that I have no particular love (or dislike) for Apache or IIS. But I don't like seeing people manipulate statistics. The graph titles are misleading, so I do not think it was intentional. I'd just like to set the record straight.