Because we provide a connector for the JBoss Maven GWT Configurator from the http://download.jboss.org/jbosstools/updates/development/indigo/central/core/ and not devstudio.jboss.com site...
<connectorDescriptor
categoryId="org.jboss.tools.central.discovery.maven"
groupId="org.jboss.tools.central.discovery.maven.configurators"
description="JBoss Maven GWT Configurator"
id="org.jboss.tools.maven.gwt.feature"
kind="task"
license="Free, EPL"
name="JBoss Maven GWT Configurator"
provider="JBoss by Red Hat"
siteUrl="http://download.jboss.org/jbosstools/updates/development/indigo/central/core/">
<iu id="org.jboss.tools.maven.gwt.feature"/>
<iu id="com.google.gdt.eclipse.suite.e37.feature"/>
<icon
image32="images/jbosstools_icon32.png">
</icon>
<overview
url="http://www.jboss.org/tools">
</overview>
</connectorDescriptor>
... we end up providing metadata links to all the upstream eclipse.org sites that make up Indigo.
Out of the box, this is what's available in JBDS for updates:

But if you select the JBoss Maven GWT Configurator connector, you get this:

