You may already be aware, but even though you have Update 3 you will still receive OTA updates like this HTC one you just mentioned. This will be a firmware update for your HTC phone rather than an OS update (like Update 3 was).
Verizon not long ago started issuing updates OTA, there is an article here about it. There was no info regarding what is included in this firmware update though.
One thing I noticed, when I read about Update 3, it said that we were supposed to be able to charge with the phone off and it never worked for me. Now it does. So that was definitely part of the update.