Question on docs - Topology planning

[David Jencks]

I was looking at the 2.1 docs at http://cwiki.apache.org/confluence/ 
display/GMOxDOC21/Installation+and 
+configuration#Installationandconfiguration- 
Changingthedefaultportnumbers

and saw the section on topology planning.  I don't understand some of  
it.

The two tier example differs from the three tier example only in  
missing the database.  This seems wrong to me.   I thought two-tier  
normally referred to the situation where the web layer and ejb/ 
business layer were in the same server and three tier referred to the  
situation where the web layer and ejb/business layer were on  
different machines.  I kind of doubt there are many useful  
applications that don't use a database of some kind, especially ejb  
applications.

Furthermore I thought that it was widely believed that three-tier  
solutions are usually a bad idea compared to running everything on  
every server in a farm or clustered configuration, so I wonder what  
the evidence for advantages to three tier is.

Is there some performance data demonstrating that serving static  
content from httpd is faster than serving it from jetty or tomcat?   
I'm certainly not a web designer or administrator but it would seem  
to me that you'd want significant speed improvements to counter the  
nuisance of having to manage your web site in two pieces.

thanks
david jencks