--- why is that bad to be tied to JBoss?
Being tied to a single app server is always a bad idea. The biggest reason is that by tying the implementation to a single app server, in this case JBoss, you are greatly limiting the potential audiences. The majority of java sites being run are NOT running JBoss, and thus they are prevented from using the dependent applications also. And, the answer is not as simple as saying "well JBoss is free, so anyone can use it". Despite it being free, most corporations and large java web hosters shy away from JBoss.
Not being tied to a single application server is a HUGE advantage for the JLCP effort.