Taugrim made a post about horizontal scaling in Guild Wars 2 via content that can get replayed "forever" in the case of WvW and structured PvP. The post got me thinking about GW2’s progression and how to really define it.
Taking into consideration what I do know about the game via reading and playing one beta weekend, Guild Wars 2 seems to be a game with both horizontal and vertical elements.
The more traditional and vertical progression is still alive and well in GW2 in the form of character levels, unlockable "traits" that you need to earn skill points to purchase, gear with stats and level ranges, and level ranges on the PvE zone content and dungeons.
The horizontal progression comes in with the automatic downscaling of player level so you can play in lower level zones. This essentially widens the areas you can PvE in rather than having to make a choice along the way. Technically, you could quest in a particular zone over and over and still progress in the game, but how long would a person conceivably do so? At some point, players will tire of the content and a game expansion would have to be released to bring the PvE’er back. Even with dynamic events in the PvE zones, the events are not infinite and will eventually be experienced by all.
As Taugrim points out, there is more opportunity for horizontal scaling in the PvP portions of the game. All players in WvW are bolstered to level 80, but there are still some vertical elements here as you still need to unlock your traits. You can earn those traits in the Mists and gain experience just like you would through PvE, but there is still a disadvantage for those who aren’t "true" level 80s. Aside from that, you could play in this area indefinitely and have different player-made experiences, and with multiple profession types.
Structured PvP (or what would be the equivalent of battlegrounds or arenas) takes away the disadvantages by giving everyone access to the same gear and traits upon joining. As far as I can tell, the only real progression in structured PvP is to gain Glory. You use Glory to purchase different gear skins, but not more powerful gear, therefore making it purely a bragging right.
This horizontal scaling seems to go hand-in-hand with player generated content like PvP. It leaves me with the question of what will happen to players who really don’t PvP at all? With no raiding to fall back on, they may leave in droves once they’ve experienced the PvE content with as many professions as they care to create. That would not bode well for life out in the lands of Tyria. Our hope rests with Arenanet seeing the trend and counteracting it, if indeed it becomes a problem at all.