While you might like iTunes, having a database (which is all iTunes is) has advantages (and disadvantages) over a file file system like a media box. Its allows you to have apps, and drm, (so you and buy/sell things) metadata in a easy interface. Most of the alternatives are not as easy to use and don't have the same functionality etc.
Also you are replying on the manufacturer to update old models with the latest version of the apps as they change. Or new file formats. At some point they'll drop support for older models. For example mine got an updated browser which now can run RTE player website. Badly but it works. Previously it didn't. But theres no Player App on the TV. The YouTube client on mine is quite limited.
Having an external box, or computer to do this means you can update that, which is a lot cheaper than replacing the TV. They also get updates quicker.
Most of the stand-alone boxes out there aren't updateable either, but at least they're cheap and work on any TV. The newer Android based ones are gaining popularity because many of them are fully updateable, and in many cases have all the functionality of a PC/tablet using a TV as the display device.
I had in my head XBMC or OpenElec on Rasberry or an old PC as HPTC.
But for the non techies Apple might be a easier if more expensive route. I know one person who while highly technical just gets everything through NetFlix or the iTunes store. They are willing to pay for ease of use and the experience.