Ret's survivability is great in PvE with no priests or warriors to remove your shields. High end PvP Arenas are another thing. If you think your 10 second divine shield is going to buy you 10 seconds of self healing or pitiful half damage you have another thing coming. Divine Shield is like blood in the water for good 5's teams and they will get rid of it (you see any top 5's teams without priests or warriors?) in 1.5 seconds or less and finish you off.

Even with Sacred Shield and Divine Sacrifice in their current form (Both are getting heavily nerfed) 5's teams don't want ret pallies because the little utility they bring to a group doesn't compensate for the fact that their single target PvP damage is track compared to Locks, Hunters, Warriors, Rogues, Shaman, etc and their PvE build single target damage is way too slowly building to be effective.

Seal of Command is an AoE seal - it's great for getting big DPS numbers in AV or clearing trash but in arenas it is completely inferior to spec'ed and glyphed Seal of Righteousness.