Web applications are a little bit different in that the web server deals with multiple, unrelated clients. If you are looking for a pattern, it is not enough to know that page Y followed page X -- you also need to know whether those events occurred in the same session. Sometimes this information is available in the logs; sometimes, not. Of course in a NAT'ed world you cannot necessarily rely on the client's IP address.
Log analysis and automata reverse-engineering are also useful for load-testing, except that instead of analyzing logged events, you generate those events in proportions and patterns that resemble what you see in the logs.
Finally, if you want to reverse-engineer an application's behavior from its outputs, you can better be confident that the application is mostly working.