I'd say 1 is unlikely because the installer will be potentially huge.
Unless the installer knows how to detect the OS and download the appropriate library off the Web.
I guess the other question is whether the binary distribution will come prepackaged with the APR native libraries. That would necessitate different downloads for different OSes.
I guess the way to look at it is what is the simplest thing for JBoss vs. what is the simplest thing for the end user. I'd say the simplest thing for JBoss is to make the end user download and install the APR binaries themselves. The simplest thing for the end user is probably to have a specific download for their OS (or if they're using the installer to have it auto-detect and install the appropriate binaries).