Actually, your accrued XP becomes run-off when the level cap is raised. Run-off that filters into the little known XP Wells that dot the countryside. (What? You thought those were oases in AO?) XP wells are the source of all the XP you gain in the game. Without run-off, the wells would dry and no one would be able to level. Ever. Again. See? It's just part of the big XP Circle of Life.