The File System Shield doesn’t scan “everything” - unless you change some of the settings.

But yes, these two shields (and IM Shield as well) are very similar. However, since P2P and IM Shields target specific programs (or more precisely, folders/files), they can use higher sensitivity for the files they scan - scanning any type of file, unpacking all the archives. If you set the same sensitivity (scanning all files, unpacking all the archives) for the File System Shield, it would probably kill you system during heavier file operations.

So, you can imagine P2P and IM Shields as special configurations of File System Shield for specific folders.