Why does HTC Incredible not update?
If you have installed a custom recovery (Clockwork or other) you won't be able to install the OTA update. You have to be stock ROM, with stock recovery in order to install OTA updates.

I am assuming that you have rooted and installed a custom recovery since you listed rom-manager as a tag. 

If you want the update you will first have to get back to stock recovery and rom. Your best bet at this point is to install a custom ROM that was built from the latest update. That should stop Verizon pushing the update to your device.