why does and EBS volumes mounted in an Ubuntu 12.04 EC2 instance as /dev/sdh1 appear as /dev/xvdh1?
There's nothing broken, so there's not really anything to "fix". This change (/dev/sdX to /dev/xvdX) was made in recent kernel versions (perhaps the 3.x tree? I can't recall specifically at the moment). EC2 hasn't yet changed their terminology to reflect the change in device naming conventions, as that would confuse all those who are running older kernels. Eventually I suspect they'll make the change, but it could be a while.