1. The streaming isn't system wide. Developers need to incorporate the streaming ability into their apps whereas Apple has it builtin to the device. 2. My parents are unable to understand the concept of "flinging" content; they want it to be a DVR-like device. The AppleTV allows them to rent, purchase, or view previously obtained iTunes content. 3. Music sounds terrible through it. It lacks an optical audio out port so it just uses the TVs speakers which are obviously not great. 4. This is probably a personal issue, but Chrome tab streaming constantly drops out after a short period of time. I've yet to get it working fully. 5. AppleTV can support games being flung to the TV while using the iDevice as a controller. This isn't a selling point, but I'd like my N5 to do the same. 6. My TV (while being a 40" 1080p flat screen) is lacking a USB port so I do have to plug it in. 7. Am I missing where I can stream my Android device's OS on the screen? I know iOS allows you to stream the entire device's OS so you can give presentations and the like.
There are many, many things the Chromecast can't do. It's saving grace is its price point which lessens peoples' expectations but I wouldn't start saying the AppleTV should aspire to be it.