I'm pretty sure the reason 8 track was even invented was so that you could listen to music besides the radio in your car. You could not possibly have a record player in a car. The use in the car was the whole reason they took off, though they did offer home players.
If you think about it, why do we have seperate console and handheld videogame systems. Why wasn't the Game Boy just a handheld NES? Well NES carts are too big for starters but, ignoring that, shrinking the hardware into a handheld at the time would not have been cost feasible and would have devoured batteries. That's why the Game Boy had to be scaled down and thus needed it's own format. The Game Boy even had the same exact button layout as the NES. It was entirely technological limitations that established the seperation between consoles and handhelds. Otherwise the TurboExpress would have taken off and Sega would have bypassed the Game Gear entirely in favour of the Nomad.
Keep in mind that eventually downloads are going to be the future so we're not even going to be limited by the size of the media. Both handhelds and consoles can connect to the internet. In terms of specs the 3DS is actually SUPERIOR to the Wii! So what keeps these things seperate? Well the 3D of the 3DS cannot be replicated on a console without the purchase of a very expensive TV. The dual screens and touchscreen are not available YET but will be when the Wii U comes out. The Wii has motion control which, in the "waggle the remote" method, is not feasible on a handheld. Kinect would also not be possible on a handheld. But are any of these mandatory features? 3D sure isn't. You can turn it off on the 3DS so there is no reason games could not just offer it as a feature that you can only see with a portable model or a 3DTV. Kinect is an optional peripheral that could just be something that only works on in a home setting (it would still connect to your portable model for when you hook it up to the TV). Despite Nintendo's attempts, the remote is no standard and the Wii U proves it. Like Kinect it can work fine as an optional peripheral that can still work with the portable model when it is used in a home environment.