Can you launch an updater from within LR4? That should show all updates for that software including CR. I have PS CS 3 and 6 installed on my Mac and the Updater from Adobe that came with CS3 does not show any CS6 updates. So make sure you launch the right updater.
Btw, I am only guessing that CR7.3 is missing from the symptoms that you showed us. I don't use LR nor Windows.
When I do click update on LR4 it says it it's up to date and there are no current updates.