Reason for level cap increases is simple, you don't want to dump 20 new abilities per class on a player when they hit cap
By increasing the level cap new abilities can be added gradually. On the gear side of things, if they add a better piece of 50 gear, why bother getting the next best piece? Raising caps has it's place in an MMO, as content, gear, and abilities are being added as the game development progresses over many years.