The main volume keys will still doing the same job but what I talk about is using this keys for long time may be case some damage
The Idea is put away your fingers from volume key and power key as possible
That's what I'm talking about
That's not a bad motivation - even though the keys on the 920 feel very very sturdy, I can't imagine them breaking. Don't forget, phones are meant to be used, I intend to use my 920 for years, but I guess I'll be sporting another device in a year or two
They keys feel sturdy enough to bear with a user so long.
You may also get what Byobg mentions, accidental hits. I had this with my iPod video often - and then you'd blow up your ears! So besides aesthetics, there are more motivations to not have a touch volume control. Furthermore, if you're browsing or writing an e-mail, you need to do to switch back to the Xbox Music app, then the physical keys are much easier then, as you can stay in the app.