I believe this is by design so you don't accidently hit the power button and the screen on. The camera button is obviously higher because you have to half press it to focus the shot before you take the pic. I had the same issue, and ordered a replacement, but the replacement phone was exactly the same. I've found that after a while you get used to it.
I've also noticed that the button is not located in the center of the side of the phone, but rather, more towards the top, who initially threw me off because I would aim for the center of the side. That's just me though.