The official position from LG support is that this is controlled by the app developer and they would have to build the app and submit for webOS. The request would need to be directed at the developer of the app, similar to how app developers submit their apps to iOS and Android. Contacting HBO support and they push back towards LG as having to build the app which is not usually how it goes. The app developer would download the OS SDK and build their app. If LG doesn't pre-install the app, it needs to be submitted to the app store.
So in a nutshell, if you want an app, contact the app developer/company to build it. However, I'm sure there are many others who are asking for this and it wouldn't hurt to contact HBO
HBOGo / SHOWTIME Anytime
in LG webOS Wish List
Posted
That's true, however, LG could vastly speed things up by officially contacting HBO and ask them to work on their WebOS app.
I have already contacted HBO and it wouldn't hurt if you at LG can do the same as well... thanks.