With "The New iPad" WiFi only, Netflix never makes it up to 720p, I notice little boxes on the screen, and HBO Go is worse, sometimes even going to "Audio only" mode for a couple minutes. But, the Trailers app (movie trailers) and iTunes preview button for movies both always load in HD. Does anyone know if this is intentional with the apps? For what its worth my desktop can run netflix and hbo in HD just fine at the same time so it isn't my connection or the other company's servers being too busy.
The newest update for the IOS version of Netflix only added rentina support for menus and such. The content itself is only streamed in standard definition for the time being but adding HD video is something Netflix is planning to do. They have no set date for when they are going to add the ability to stream in HD at the moment though. I've never used HBO Go so I can't comment on that sorry.
According to yahoo news HBO Go is still in SD for the IPAD too. So is Hulu Plus.
HBO Go on Wifi is already HD at 720P. Rumor of 1080P for the iPad3 on Wifi is expected to be available in October. On 3G/4G/LTE the video resolutions stays below real HD to conserve bandwidth on your data plan. HBO Go already does 1080P with 5.1 audio on Roku2 and Samsung devices.