Without having tested Retribution on my paladin, I have personally witnessed that Retribution can put out more DPS pressure than Prot in arenas (where both players are equally geared and skilled).
The consistent damage increase from Sword of the Light (25%) causes Crusader Strike + Judgement + Templar's Verdict to put out significant pressure over a span of time, perhaps even outweighing the weaker Crusader Strike + Judgement, and Holy Wrath + Avenger's Shield from Protection (Assuming the Avenger's Shields aren't consistently hitting 2+ targets).
I don't have numbers to back this up (because so few players actually have a fully geared Retribution paladin), but it's worth considering that your damage can be more than decent as Retribution spec.
That being said, Protection has an extremely powerful control of the battleground, especially in teamfights.
Play your style. Retribution is far from non-viable.
Oh, and one more thought - next expansion, Blood Elf Retribution Paladins will be able to Templar's Verdict + Crusader Strike + Arcane Torrent + Crusader Strike + Templar's Verdict, effectively reducing the TV cooldown for level 20's to 4.5 seconds. Which, considering the acquisition of a holy power charge on Judgment use isn't until later levels, is quite significant.