If anybody has been watching HBO GO on a Surface RT or Surface 2, that had to be an accident.
HBO GO feeds their content to an app designed for the mobile device. The HBO did not make an app for Surface RT/Surface 2 (ARM based) tablets.
If you want to watch HBO GO on the tablet, you have to contact HBO and ask them to make a Metro UI app. They are the ones who provide the video feed, not Microsoft.