Although you can do mainly most of the view part through jsp there are enough reasons to use Velocity and/or FreeMarker.
Both Velocity and FreeMarker templates can be packaged in a JAR. Struts plugins are distributed through JAR. One cannot distribute JSP's in JAR that easily. This can be one of the reasons why Velocity or FreeMarker may be used. FreeMarker is more advanced then Velocity. So FreeMarker gets the upper hand. Even WebWork developers have switched from Velocity to FreeMarker.
