A lot of demo applications (e.g. Seam applications) that work on JBoss AS 6 and use the built-in datasource assume to find it at java:/DefaultDS. However, AS 7's default datasource is available at java:/H2DS.
To retain backward compatibility with pre-AS7 JEE applications, I think it's a good idea to bind the default datasource to java:/DefaultDS as well. Otherwise, the applications will:
a) need a separate build profile for AS 7
b) fail to deploy