Web Age Solutions are wrong.

You can't compare Tomcat against JBoss et al, as the former is merely a subset of the latter.
Even on the Tomcat site, the first paragraph states "Apache Tomcat is an open source software implementation of the Java Servlet and JavaServer Pages technologies".

This article is nothing more than an attempt to discredit a good project and their contributors. :(

Though Tomcat is just a implementation of the Servlet and JSP technologies, it is a great entry point for developers getting into Java EE and enterprise solutions.
Once you get to the limits, it is merely a step up to a full fledged application server and still retain your knowledge gained from Tomcat as useful.