I was having the same problem with a blank screen on the Updates tab in the App Store on a 3rd-gen iPad. The following did not work for me: normal reset, hard-reset, killing the App Store app, clearing the Mobile Safari cache.
What finally did work: killing every app running on the iPad (including the App Store app). Then when I re-launched the App Store, I was able to see and download all of the updates.
My impression is that the problem is on the iOS device and not on the iTunes server. I setup a HTTP proxy to watch the traffic from the App Store app back to iTunes, and it is making a request back to iTunes and getting a valid response of the apps that need updated even when it was displaying a blank screen. My guess is that there is some other app on the iPad that is using up resources which interferes with the App Store displaying the updates, and when I finally killed all of the running apps, that freed up the necessary resources for the App Store to resume normal operation. There is probably an app which is just for the iPad, or which behaves differently on the iPad compared to the iPhone, which is why this problem only manifests itself on iPads. (sorry, I didn't keep track of which apps were running prior to killing them all.)