Sky go extra is just an easy way for SkyUK to enable extra services including Console usage which is HD...
but SkyUK insured that the service is treated as a new service level by insuring that the devices run the "TV from Sky" service app no Skygo app...
Mobile devices run sky go in SD
Mains connected HDMI devices run "TV from Sky"... Yes for the lesser equiped users they should have changed the console activation part to another name but its still the same device management system that allow consoles and mobiles...
"TV from Sky" is activated by getting Sky go extra which enables console HD "catch up and pre recorded" content in HD as an extra to the mobile SD service...
Untill Sky go extra is renamed some user will be confused as to why Consoles which are not mobile devices are included... My surgestion has been they drop the "GO" from the service... "SkyUK Extras service subcription"