While arguing with Jeramyu in the other topic, one of his sentences jumped at me, where he basically said that while the Reaches ending does not ties directly to the plot it is still a truth (as a concept in this case)
What if each ending represents a different kind of "truth" Rhue reached?
In the Reaches ending, Rhue finds Truth as a Concept
In the Lexus ending, Rhue finds emotional Truth, or in other words, the key to Happiness.
In the regular ending, Rhue has found a Physical Truth, one that belongs to his world, the one he was seeking.