A Sar file can contain jars, wars etc. JBoss has integrated tomcat with its own sar file. Why should the ROOT.war be outside this sar file? If you want to remove tomcat, just remove this sar file.
I think you should do more digging into documentation about what a SAR is, what exploded archives mean etc..... If you already know them, I apologize.
Bottom line: It is far better for a service to contain all the configuration/apps etc within, than have them scattered around.
There is no strong argument for the ROOT.war being in the sar other than its integrating with some of the tomcat content. The downside is that if you want to override the root context deployment it can be confusing where the existing root context war is coming from.
I'm aware of what a SAR is and can contain (no apology needed, I wasn't as clear as I could have been.) The reason I bring it up is that conceptually the ROOT.war should work under JETTY, Tomcat, Resin, or just about any other servlet container that is used. And it seems like if it were under deploy fewer users would be confused by it. (Albeit there is a strong argument to just RTFM and figure it out.) Just my two cents.
True, I forgot that ROOT.war references the Tomcat status servlet.