'Bright Dock' is free, accomplishes same thing
found this thread, I wasn't happy with KeepScreen as I didn't want my phone to stay lit when only plugged in, not in a dock.
DockAwake seemed like exactly what I was looking for, but I did happen upon a free app 'Bright Dock' that works well for me.
It disables the auto-off when in the dock, and optionally only disables it if you are in a 'charging' dock - eg if your dock is plugged into you pc, and you shut the pc down, you phone will still timeout & not kill the battery.
Nice :)