Here is a LIST:
1. Wakes the phone from sleep
2. Closes Apps
3. Moves back to the home screen
4. Opens Spotlight from the home screen
5. Brings up the last used apps list (iOS4)
6. Displays the iPod controls when the phone is locked
7. Activates the Voice Control
That's just the ones I know about.
So this reason they have is just pointless, let the app developers do it and make the software work the way we want.
So if you have version 1.2.1 of Camera+ you can enable the Volume Shutter by going to this address in Safari on your iPhone camplus://enablevolumesnap and if you get confused by using the volume buttons as a shutter button you can disable it by going to this address camplus://disablevolumesnap
I've done it and it works a treat.
Steve Jobs you know that guy on the big screen in the Macintosh 1984 add? That's you that is!!