Only some HBO channel show up in HD

HBO Family HD, Zone HD, Sig HD, HB0 W HD and HBO 2 W HD are only available if you have a Contour receiver capable of MPEG4. See here for what those channels are marked with a triangle symbol, and at the bottom it says:

"Contour HD Channels, if included with your service level, require rental of a Contour receiver or Cox-provided CableCARD™ together with a certified compatible CableCard retail device capable of tuning those channels."

and others they don't carry Omaha dropped HBO Comedy HD due to low viewership