Firstly, it should be mentioned that there are roughly two types of installations on the Mac:
1) Drag and drop to the /Applications directory (you'll mostly see this).
.... Installation/uninstallation is as easy as copying/deleting it.
2) MPKG files (like MissingSync, Parallels, etc.)
.... Required if other components are needed (e.g., extensions).
Luckily, OSX (and Linux/UNIX for that matter), uses files for everything. Windows uses a registry, which I really wish Vista moved away from. Personally, I hate the Windows registry - besides, all Windows apps use the registry in different ways. It's not consistent.
As for your question, the OSX /Library doesn't necessarily equate to the Windows registry, since the /Library holds a much broader scope of files. At least there are subdirectories to tell ya what they pertain to.
