I see more games trying to avoid having their earlier content become completely irrelevant while improving their endgame. You do this by having a version of the old content that scales to the new level cap; games without levels have this mostly baked right in anyway. Feel free to comment with your favorite game; World of Warcraft and The Lord of the Rings Online™ are the ones I know best for having another version of older dungeons available at the level cap. Borderlands had its own version: after you beat the game the second time, everything levels to the cap, from the final zone to the first skags.
City of Heroes took a different approach, and it seems to have worked against them from many players’ perspectives. Everything scales, and you can always drop back profitably, so every instance remains relevant as you level. Everything is endgame content and leveling content. Perhaps because of that, City of Heroes has never built much that is endgame content in name. A favorable interpretation is that very little is held back and hidden behind a grind; a less favorable interpretation is that there is little new to do at the cap, which quickly becomes “there is nothing to do at the cap.” Those who took the latter interpretation generally unsubscribed. The illusion of scarcity is an important marketing principle.