I had the similar problem in 4.0.0alpha - it can not instatiate classes from WEB-INF/classes during servlet deployment, but can instatiate them if they are packed in jar in WEB-INF/lib.
In 3.0.0 version JBoss could intatiate classes from WEB-INF/classes.
I didn't try pack them into jar so I don't know what would be so far but I believe you.
As for me I had so many troubles with 4.0.0alpha that I decided to wait for official release and return to 3.0.0 version wich seems to me more or less working. Even 3.0.4 I consider to be worse - it can not unlock beans locked (what I don't understand) and my applications that worked in 3.0.0 don't work in 3.0.4. Sorry if I didn't help you. I can advice only to take 3.0.0 and put your classes in WEB-INF/classes. It works for me pretty well.