I've been thinking about ways to refactor a fairly expansive class/utility library I have, and one thing I think I want to do is split off any higher-level helper utilities that introduce new dependencies. I read some previous questions here, and one that I particularly noticed was a comment about how Microsoft freely uses namespaces across DLLs. The example given was System.Web - it's in the base framework, but there's also a System.Web.dll that adds more functionality to the namespace if you want it.

I also noticed several other System.Web.* DLLs available, and I was wondering if there's a reason why they wouldn't be combined into a single DLL. Could it be that they have their own individual dependencies and Microsoft (like me) wanted to separate assemblies along those lines? Or is it for easier maintenance? Something else entirely?