Unless you need some module specific to Apache, there is absolutely no reason to use the Apache/Tomcat combination. I was just looking at this
Tomcat FAQ on Tomcat performance which indicates that Tomcat can equal Apache for serving plain html under some conditions. One of the links there lead to this quote:
I have a server right now that has 20 distinct instances of Tomcat on
it, is serving a fairly sustained rate of 500kbps-1.2Mbps with several
hundreds of open connections. About 1.3 million hits a month, but hits are
misleading. CPU load (dual P3-1.2) is averaging 31%. 4GB of RAM, memory
used averages about 2.2GB. Red Hat 7.2, Tomcat 3.1.
For security, Tomcat offers very fine-grained security via the
Java SecurityManger mechanism.
Bill