The issues I've presented demonstrate some of the larger issues you would have to contend with if you choose to administer your own webserver, but there will most certainly be many smaller issues to contend with. Given all of these potential pitfalls, extra costs and added level of difficulty, why would anyone ever manage their own webserver?
There are three major reasons why you would want to run your own webserver. The first reason is public perception. If your company sells servers, you want your website running on one of the types of machines you're trying to sell. Even though there's extra cost and effort involved, the benefit you gain by having a server that stands as proof of concept will far outweigh the costs over the long term. The same kinds of public perception issues apply to any company or group that is technology oriented. But public perception can't possibly be the only reason people run their own webservers. There must be some other motivation.