Can you easily read upside down?

Yes, pretty easily (just checked).

I'm asking because neither of the upside-down face illusions seem to "work" for me. (I was immediately startled by the deformed version of Margaret Thatcher.)

So the deformed Thatcher picture wasn't any more startling upon turning the image over? Well, you may have some unusual aspects to your visual cognition. Try it with some more faces and see if the same thing comes up.