When they designed the user interface, they tried both horizontal and vertical, and decided that horizontal worked much better on this particular player. Many people have speculated that they'd like vertical better, but they're saying it without actually having seen vertical menus implemented on the player, so there's nothing to compare it against.

The Rio Receiver has vertical menus, and I'm not sure whether I like them better or worse than the car player's horizontal ones. I know I get confused as to which direction I should turn the knob on the Rio Receiver, and I don't get confused on the car player. I know that my selections on the car player are quicker and require less fiddling. But maybe that's just me.

I could have sworn that one of the empeg guys said that when they implement the Soup views on the player, they would make those vertical-scrolling. But I might have been imagining that.