Why do the tournament rules require opaque card sleeves? Does this mean opaque backed or should we take it as written and use sleeves that no one can see through?

Use sleeves that no one can see through. As the FFG promo cards have different card quality that can be detected through clear card sleeves, the rule on non-see through card sleeves alleviates anyone from being able to tell what cards might come up next.

Just the backing needs to be opaque.

The idea is each print run (within a set - Awakenings has already had at least two print runs if not more - or across different sets since no two sets should be printed at the same time) risks having slightly different image resolution, brightness, saturation, card thickness, etc. Sleeves that you cannot see the backs of the cards through removes this potential printing issue from providing a distinct play advantage to players.

If sleeved, why do character and battlefield sleeves need to be different than deck sleeves?

20 minutes ago, wakefieldbw said:

If sleeved, why do character and battlefield sleeves need to be different than deck sleeves?

I assume so that you don't confuse the material and somehow lose them in your deck.

Also so you buy more FFG sleeves...

The funny thing about it is that the rule just says opaque sleeves. Not opaque backed sleeves. So I think if you follow the written rule you just have to guess what cards you are holding .