One thumb use (Go and watch people who use touchscreen phones, no matter which brand: They'll always hold it in one hand and tap on it with the other hand.)
Tactile feedback I need to be able to operate the device without looking at it. It's a mobile device, so I do things with it while I walk, while I talk to somebody, etc. With hardware buttons, I'm always certain what to do: One to the left, one down, press. Center, press. Quick look at the display, one up, press. You cannot do this with a touch screen.