Physicists actually use spherical cows-- it's a useful simplification to make calculations tractable. A phib as used here is more like the common "imagine a trampoline with a heavy ball on it" explanation of gravity that I always hated growing up. (Mostly because it's self-referential, but it's other kinds of wrong as well).

Did you read his book? I'm considering it... This blog entry refers the reader to the book for an actual explanation. Annoyed me a bit since I was hoping to find an explanation in the blog entry itself. He says it's too long.