It really depends on what they sell
A STB is limited in the amount of improvement it can make on the TV's interface, since you still have to deal with the crappy way TVs keep switching between inputs and switching between channels separate.
Consider a TV hooked to an antenna for local HD channels, along with a cable or satellite box, plus several other inputs (Blu Ray player, and game console, let's say) This is not an uncommon setup in the US, at least. So if you use it on the game console and then turn both the console and TV off (standby) when you're done, when you or someone else wants to use it to watch a particular program you must:
1) turn on the TV
2) select the correct input on your TV (perhaps having to ask if it is not your TV)
3) turn on the cable/satellite box (if necessary - knowing that hitting power turns it off if it is already on)
4) know whether the program you want to watch is on antenna or cable/satellite
5) know the channel number of the program you want to watch if it is on antenna
6) enter the channel number or select it from the guide if on cable/satellite
Now for everyone reading this, this isn't difficult. We're Reg readers, by definition among the more technically literate. Even so, if we'd been asleep for 30 years even we would need some help doing this the first few times. Many of us probably have parents who aren't quite so technically capable and the above would be too complicated for them (despite my dad having a PhD from Berkeley and writing FORTRAN programs 50 years ago, he's never quite got the hang of modern consumer electronics and Windows) Fortunately my parents have only cable boxes, so they never need to switch inputs on the TV, and thanks to me cleverly configuring the cable remote for a TV that is the same brand but different model, the cable remote can turn on/off the TV and control its volume, but can't change inputs or change the TV's channel so it is pretty foolproof unless they find the TV remote :)
Let's imagine a TV where when you turn it on you have a little menu that offers various choices to go to "games console" or "Blu Ray" or some of your favorite channels, or a collection of previously recorded programs on the DVR, or a guide which integrates all the channels available from antenna, cable, satellite, Internet, whatever you have, into one place. You select it via a touchscreen remote or possibly your voice) The TV actually uses the HDMI CEC protocol that only Sony seems to know about, so when you go to the games console it turns it on for you, and when you select something else it turns it off for you so you never need to fumble with multiple remotes or teach one remote how to control other things. The TV and remote doesn't have a concept of switching "inputs", or a concept of keying in channel numbers. The end user has to enable a configuration option to even SEE channel numbers. When you are done watching what you wanted and want to go to something else, you go "home" on the remote/voice similar to an iPhone's home button, and you are back at that menu again.
Is this what Apple's TV will be? Probably not, but IMHO it would be better than the interface on any TV I've ever seen. You are free to disagree, of course, as it has some obvious problems. Mainly, that it wouldn't work with every possible piece of equipment you could connect to it like today's TVs do. Not even close. This is the reason why no one sells a TV that works like this, but that sort of thing has never stopped Apple before. If it was successful devices like Tivo, Xbox and Directv receivers would be built/modified to work with it, just like the ecosystem that grew up around the iPod. They'd all still work with other things, and when Google/Samsung inevitably did their own version of this, they'd work with them as well.