I\'m writing this code in a Console Application targeting the .NET Framework 4 Client Profile.
this.container.AddFacility(
f => f
Some of the appenders depend on System.Web such as the AspNetTraceAppender. The only other option available to the developers would have been to split out components that don't depend on the System core into separate assemblies but that would have broken the beauty of log4net in that it is so simple to use. Additionally at the time of writing log4net I don't believe their was such a thing as a Client Profile.
Since log4net is open source there is nothing stopping you from downloading the source and removing the offending classes and creating your own Client Profile centric log4net assembly.
http://www.thecodeking.co.uk/2010/08/making-log4net-work-with-net-client.html
Here are my thoughts: Log4Net uses System.Web because the developers decided this was the best option.
If you don't want this weight, consider a logging project that does not require System.Web. There are other options.