I presume this means the Apple TV will be able to control set-top boxes, surround sound systems, etc. connected to the Apple television if they have the api. I hope it also means an app ecosystem for the TV, so that developers can extend functionality.
IF the boxes are made to take those commands. That could be what this API is about.
That said, it could be for the set top box not a 'real' TV. Consider the market, consider the licensing they would have to do to put in TV tuners etc. Few folks would buy this TV if all it can do is the same stuff that the set top box can.
So they make a revised Cinema Display lineup that is their test bed for the Retina Display, has at least 2 size choices and includes HDMI etc for using with a blu-ray, the ATV box, computer, game consoles etc.
They create this API and perhaps others that allow you to use bluetooth or wifi based controllers in your apps so that you can make a game that uses a 'Nintendo' style joystick and button pad for those that want physical controls. Maybe even a Wii like steering wheel for your Real Racing HD.
And yes perhaps they allow developers to create games designed to go right on the Apple TV box. So you can buy Real Racing and rather than Airplay it is there on the box. Perhaps they might even bump the next box model up to 16 GB or even 32GB if the component costs are down enough to keep it at that $99 model (or maybe they keep that one as it and make an Apple TV plus that is the higher and can take the games for like $149).
Who knows maybe Tim Cook has convinced Nintendo to release their classic titles for iOS and he will invite the head guy up to introduce that release. If it is well created I'd go as high as $9.99 each for the original Super Mario trilogy. Especially if I had the option of using my iPhone, iPad or a 'real' controller. Hopefully they would be Game Center linked and sync scores and levels across the system. So then if I'm traveling and I use my iPad version to get 4 more stages ahead I can pick up there when i'm back home.
And so on.
Also more content deals need to be in the system. Get the back seasons on the store, get the prices knocked down $1 across the board for tv. Features on the movies. Extras working on the ATV and iPad. Credit when you buy a movie inside those Warner Bros apps, the last of the movies in iTunes in the Cloud. All shows on the store after first OTA and at 720p at least (1080p also preferred) and so on. Which really just needs the box, not a real TV.