I'm no expert in this field but here I go:
I believe that people tend to use Apache for the following reasons:
1. They feel it is a faster way to deliver static content (JSP are dynamic and require a WebContainer).
2. They need a legacy CGI engine
3. They feel that offloading the static content to another box will free more resources in their webcontainer - i.e. their system scales better.
4. They are using some kind of security set up that involves Apache, and want to direct every request through it.
5. They are comfortable using Apache and don't want to make the investment of 'porting' their static content to a webapp.
6. They are using apache for some sort of load balancing - scalability once again.
If all your content is dynamic and you do not require apache for any of the above reasons, then I do not see how sticking it between your webcontainer and your client can possibly speed things up. You are just doing more work to achieve the same goal.
I believe that Jetty (which coasted through a SlashDotting a while ago on jboss.org) is fast,scalable and secure enough to use for your static content. It has a CGI servlet (admittedly not as scalable as Apache), and h/w and s/w load balancers are available. Furthermore, using just JBoss/JettyOrTomcat without apache simplifies your installation considerably and this will be reflected in the complexity of your site and it's management.
One size never fits all and you will have to base your decision on the best info you can get.
Hope that helps,