Warhammer Online recently released the 1.4 version and, along with it, two "add-on packs". These are interesting because they don't expand the game in the traditional way, but at least one of them has a profound impact on the game.
The less important pack is a "personality pack" that gives players access to new dyes, exclusive vanity pets, appearance-modification tokens, and fancy-looking mounts. The mount is if interest because, although it shares the same stats as the mounts purchasable in-game, it costs the user no in-game currency. Sort of a content-bypass here, but a fairly minor one.
The more important pack is the "progression pack" which unlocks Renown Ranks 81-100. Renown Rank is sort of your "pvp level" in WAR, and determines how much PVP power you have and access to PVP gear. Thus, only players with the progression pack can get past level 80, and only they can buy the 80+ PVP gear. This is massively unbalancing, obviously, so anyone who plays WAR seriously will have to get this pack.
That, in itself, is nothing new or unexpected. In any MMO, whenever an expansion is released, it's generally required content. It's hard to imagine anyone playing World of Warcraft without Burning Crusade or WOLK, let alone compete in PVP locked 10 or 20 levels below anyone else. What's interesting is that this pack only ups the Renown Rank and not the actual level, which remains capped at 40. There is no new content: no new areas, no new zones, no new quests; just high rank and gear that you get using already-existing scenarios and battlegrounds.