Well, there are several criteria that go into choosing a web platform, that most people here just don't get. Stability and security are actually down on the list of priorities below functionality, cost and support. If times between reboots were so important, then nobody would run Windows/IIS for a webserver.
One server I run started out on HPUX/Netscape I-Planet server, but the app kept taking down the web server and sometimes the webserver would not restart without rebooting the entire box. The vendor basically threw up their hands at us, saying they didn't know what was wrong, so we switched it over to the other platform they supported - IIS. It has run on IIS for four years now. The app has actually taken down IIS a quite a few times too, but it was much easier to restart if it did, because of access issues. Only two people has access to the HPUX server because of some other sesitive data it contained, while all of the IT staff had to ability to go into the IIS server and restart IIS. On top of that the webserver never had to be restarted because IIS wouldn't restart. The vendor has finally worked out the bugs in this app in the last two years, and it has been stable since then.
Another server which we use IIS. We chose IIS over Linux/Apache and SOlaris/Apache because we were already used IIS for the other webserver, and nobody else besides me in the IT department has the ability to support linux/apache. This particlar app is well programed, and the IIS server has never crashed in three years.
We are replacing the server soon, and it will be moved from Win2k/IIS5 to Win2k3/IIS6. There is no good reason even consider another platform for this server because the current one we use is absolutely rock solid, and we are better equpped - staff wise to support Windows.
As for cost, in the business world, why stress over a $5000 difference in software costs, when it costs $30,000 per year for the software that runs on the web server, $150,000 a year in the salaries of the staff that will support it, and $25,000 every three or four years for the server itself?