There are a number of limitations with web stats. If some agreement can be made about terminology, the job of comparing web stats will be made easier. Web server activity is a term which describes the data collected from a server log. This does not include the proxy server activity of your visitor's ISP, or visitor activity such as caching and offline copies. Other considerations to make are measurement of different servers that you are using for your web services, and also of the proxy server used by your web hosting service.
Web servers collate log files.
The way that the log files are compiled may vary between server software versions. System administrators have access to this type of information. Reporting of statistics needs to be standardised. For example the Open Road web site has such a system. Websites which require a user to log in will have statistics as well.