Accuracy caps for everything that has an accuracy cap: http://www.reddit.com/r/ffxiv/commen...ything_coil_19. Everything else has an accuracy cap of 0. Meaning, you can hit everything else in the game 100% of the time with your base accuracy as a level 50 BLM. Every dungeon monster and boss, every CT/ST/WoD boss, all the other Extreme Primals, everything. Accuracy is a dead stat outside of Coil.
Also, people put Piety on their relic because, if you look at the monster BLM DPS spreadsheet with its crazy math (sorry, I don't have a link, but you can find it if you search), there are rotations on there that you can do with more piety that do noticeably more DPS even with lower stats (it's the F6 series of rotations where you have 6 Fire 1s after each Fire 3). The only way to get PIE on a BLM is to either meld it into the relic (very cheap) or use penta-melded accessories (very expensive). That is why people who are really hardcore about their BLM DPS will use PIE on their relic, and yes, it's totally worth it. If you notice, these people are (or should be) all dunesfolk lalafels, the best race for using these rotations due to their higher PIE score.
