While it is ridiculous, your comparisons are also a little ridiculous. Product similarity is a large part of whether something is trademark infringing.
The point is that facebook didn't invent face, didn't invent book, and didn't invent wall (not even in the ACTUAL meaning they are used in facebook itself).
If I want to create a website with social tools that for some reason involves wall or book I don't see why I have to risk to be suit based on a user agreement (that usually nobody reads).
Say that I want to open a social network for old book lovers. I can't call you the old book or the ancient book or whatever you can think of just because facebook thinks they own the word book?
Or what if I want to use the metaphor of the berlin wall to open a thematic social network for human right causes and maybe also use the idea that you can place notes on this wall?
Do you think that in that case am I actually infringing the Facebook trademark?
Yet I'm sure they could try to sue me if I'm a Facebook user and agreed to their fluff.