There are several J2EE frameworks that come into mind when talking about single and multiple access points -- for example, the Jakarta Struts project (which uses the MVC Model 2 architecture) uses a single access point, but they kind of blur the line between their front- and page-controllers.

Turbine uses multiple access points, all of which could potentially forward you through the main access point, if that is the desire of the developer or application designer.

It's mainly a matter of personal preference.