Tobold is once again complaining that Blizzard should produce annual WoW expansions instead of taking two years per expansion. I think he's a bit unduly fascinated by the $40 box with the coaster and the card that has a 20-digit alphanumeric key on it. The real question to ask is what benefit players can expect from more frequent expansions. In particular, Tobold assumes that the level cap would raise in each of the annual expansions. Does anyone actually want this?
Who wants a level cap bump?
At the risk of generalizing about a demographic that I'm not a part of, I never get the impression that raiders are super thrilled about a level cap increase. Tobold is arguing that the damage is already done by having mid-expansion gear resets, but we've been seeing those MORE than once a year, and I don't think anyone would raise the level cap that frequently.
Meanwhile, increasing the cap retires content just as surely as gear inflation does. If you're queueing up for a random 5-man dungeon, would you rather have the same list of 12-16 dungeons for two years, or a list of 8-10 that expired every single year? I've done this experiment on my Warrior, who only has access to half of the dungeons due to his level, and I'd vote strongly in favor of the broader list, even if it meant fewer dungeons overall. If you've only got half a dozen dungeons to choose from, you're almost always repeating one that you did just a day or two ago.
Finally, we come to solo content. This is the area where, as a non-raider, I should be the most solidly behind Tobold in support of the annual cap increase. Solo players got a moderate amount of repeatable daily content in patch 3.1 and 3.2, a year ago now, and have not seen anything since. However, like group content, solo content also thrives on variety. If you're pushing to produce annual expansions, whether they are five or ten levels, the trend is going to go towards producing just enough content for characters to make it to the new cap, so that you can declare victory and go work on the next expansion. This will ultimately hurt the quality of the solo experience as well.
Horizontal or diagonal expansion?
If you look at games that actually pull off approximately annual expansions, like EQ2, the trend is strongly in favor of mixing in horizontal expansions along with the vertical ones. This still retires some content - in general, players ran the content from the Kunark era (raised the cap to 80) once to complete quests and spent most of their time in the Shadow Odyssey (horizontal expansion, which kept the cap at 80 and added bunches of new dungeons) due to better loot. You would then want to add some sort of alternate advancement, but WoW already has talent trees and glyphs, and may (or may not) get yet another system in Cataclysm.
The other issue is that a horizontal expansion is generally not going to do so much for solo players. EQ2's TSO added a new leveling zone and some new reps, including a solo daily quest that dropped tokens for dungeon loot, but I didn't bother to do any of it until the next expansion arrived and increased the level cap. There wasn't really any reason for me to do so, as the previous expansion's content was enough to let me reach the level cap, and it's not like I would have been aiming to do something with the dungeon loot if I'd obtained it.
In some ways, Cataclysm may be Blizzard's attempt at a diagonal expansion - not entirely horizontal, but not entirely vertical either. There's less vertical movement, and Blizzard is using the time to polish up existing talent trees (only including five new points allows them to avoid adding a new tier) and holes in existing content experiences. That said, this expansion's longevity may be heavily dependent on players' willingness to re-roll to see how the world has been shaken up. If players tend to stick to blazing through the new stuff on an existing main, this model could also feature the worst of both worlds, leaving players done and ready for the next expansion even sooner than the previous editions.