The absence of Update tab in JCP was noticed on XP and Vista machines. The installation is not full if the system was not clean. After canceling installation Java Update leaves some registries, the comments about that was added to 6705515, see description. 6u19 b01 installs Java Update anyway, the Update tab appear after VC++ Error, but 6u19 b02 doesn't.
The same can be reproduced with 6u18 plus build, tried b74.