Is Seam a similar concept to Grails or Rails in that it is a "super framework" consisting of a number of building blocks?
seam-gen attempts to do something similar to Grails or Rails. Honestly, those other two frameworks have a better commandline tool at this point. But understand that seam-gen is really just a way to get you started with Seam, it doesn't try to write your whole application for you (something I think that Grails and Rails are trying to create an artificial intelligence programmer).
Seam goes so far beyond seam-gen that I have chapters 3 - 15 to tell you how.
Does Seam in Action make any comparisons with other frameworks?
I do a comparison at least every chapter and sometimes more.