The Microsoft Visual Studio 2005 version of the Help viewer no longer shows the default page automatically as previous versions did. Doc-O-Matic doesn't use this parameter when showing the Help file because it doesn't know what version of dexplore it launches.
To open to the default page do the following
Pass an additional command line parameter named LaunchNamedUrlTopic to dexplore.exe (that's the viewer application for Help 2 help), like for example: dexplore.exe /helpcol ms-help://yournamespace /LaunchNamedUrlTopic DefaultPage