In-Game Parser.

[Ellatrix]

ignorance is bliss

Having damage parsed (perhaps by someone else) is mandatory to be a top dps - because if you don't, you have no way of telling how good you're doing. There are zero top tier dps who have not benefited from a parser. Also no, parsers have been available from pretty much game launch, and most certainly before groups were clearing T4, which had the first real dps check.

Yoshi-P does know his audience, and he knows there are plenty of crybabies who would be pretty upset when they find out that they are, in fact, bad at their job and would be getting kicked for now obviously holding a group back. And instead of getting better, they would just quit the game and go play something more friendly, like Farmville. Though I think the devs were surprised to learn how bad some players are, given how hard they had to nerf SCoB.