Just got off the phone with HTC escalations that replicated my issue. Turns out the software options for the EVO 3D and EVO V 4G are a bit different. He was able to get HTML to work on an EVO 3D via Exchange, but could not get it to work on an EVO V 4G. The option was greyed out for him on the EVO V 4G just like I was experiencing.
I don't know of this is Virgin trying to cut corners by reducing the data consumption that is required via HTML emails or what???
Anyway, now I'm using Touchdown HD app and it's working just fine. Only issue I have with Touchdown is - it automatically downloads attachments without an option to prevent it from what I can see?