I just did this same thing on CentOS 5.1 Linux (running in VM Ware on the same Mac).
I used the same JBoss AS and Seam binaries.
I used Sun Java 1.6.10.
In this environment the iText example works.
So, this might be an Apple OS X issue.
I'm not having any problems running the iText example on OS X.
By any chance are you using FF3? I tried it with the Seam trunk, 2.0.2.SP1, 2.0.2.CR2, 2.1.0.A1, etc. and other browsers it's OK, but FF3 gives URI like the following
The same thing in IE or Safari (for windows) will give a proper URI to produce the pdf.