Well the phone is different because it was not designed to be used while driving. Compare the phone to the climate control or radio controls in a car. The radio controls are in a fixed place on the dash
My stereo has Bluetooth access, and I use my phone (mounted on a secure spot on the dash) as its head unit. That way I've got the same music options (including my entire 200+ CD library) available wherever I am. In this configuration, futzing with it is exactly like someone futzing with their stereo controls.
Now you may argue that it isn't designed for this use. However, it is far better designed for this use than most modern electronic car stereos. Many of those are designed so badly, with unnecessary extra menus, clicks, and delays you have to watch for (with your eyes), that Consumer Reports has started removing recommendations for the cars they come with.
There are a couple of options here. We can be Luddites and just try to blanket ban new things because some ways they are used are dangerous, or we can acknowledge that people will be doing it anyway, and try to do what we can to make what they will be doing safer. Standards for "car-safe" apps when hooked to a BT source would be a really good start.