I think there are two different issues: (1) there's a real difference between a laptop and a tablet, or, more generally, between devices with different sorts of input and output affordances; (2) a device may not fit exactly into any of yesterday's profiles. For that matter, even today's devices don't always fit into neat profiles or even stay the same. My laptop is a laptop, but a tablet, except when I'm eating a burrito, in which case its keyboard is less useful. When I've got my trackball plugged in, it's also a bit different, and sometimes I've got it plugged into a monitor and I'm sitting across the room, and it's a media center. When it's a media center that thinks it's a laptop, the text is too small to read comfortably.
The Unity mess is going in the wrong direction, obviously: different devices are actually really different, and it is wrong to treat them the same. But the status quo is also wrong: even the same device is sometimes different, and you need multiple UI configurations and the ability to switch between profiles based on context.
(For that matter, my laptop's headphones are too loud, and the speakers are just right, except when the air conditioner goes on and they're too quiet.)