Yep - and applications should be able to use them for their own purposes (except the power button ? & maybe also a global switch enabling/disabling application access to buttons).

Possible uses for hardware buttons:

• zoom in/out
• turn pages
• trigger rerouting
• take a picture
• start/stop/pause recording
• jump to task switcher
• toggle flashlight (long press ?)
• full-screen toggle

Every button can be assigned at least two actions (press + press hold). Of course, there are also more advanced possibilities (double-press, button combinations).

Physical buttons also have the important advantage of tactile feedback - you can easily press them without looking at the device or in adverse visual (darkness, heavy sun) and motoric (gloves, in a shaking vehicle) conditions.