I think the main issue about language is the question of who you're talking to. If you're speaking to a friend with a very weak grasp of Rationality and Probability the sentence that sentence will not make sense, and be needlessly convoluted.

To me it looks like Eliezer is trying to set up a new standard (perhaps just for this sequence) about when and how we are allowed to use the loaded words 'truth' and 'rationality'. So it doesn't make sense to try to apply this to every single conversation (especially outside of Less Wrong).