OK, you mentioned ENT needs to be re-rendered in HD. But it has been broadcast in HD since its second season and has been shown in HD on HDNet the last few years. What I saw on HDNet doesn't seem to be uprezzed. at least not the episodes from the last 2 seasons (which I saw on a bigger and better TV set).
It will be a business decision CBS Home Video will make whether they will pay for visual effects to be rerendered and edited in to a new HD master before the Blu-ray seasons are released. They may feel not enough people will purchase it on Blu-ray to warrant the additional costs.
It is far cheaper for them to do audio commentaries as new special features.