Something I thought of while reading the article, and which semi-ties in with LTK_70's thought for limited lifespans...
Kingdom of Loathing has a re-incarnation mechanic, which is in and of itself necessary for advanced players to minimax their characters. Several of the quests have mutually exclusive outcomes, so you can only really collect all the best stuff by trying different solutions to the same problems.
One of two things then: either the greased leveling curve following expansions is indicative of just how useless the early level content was to start with (when lacking large numbers of simultaneous users at low levels), or the company assumes that its user base is static, and the only people going through low-level content are existing users at or the near the level cap, who have already experienced the content. The KoL approach could be really useful here, in that if you're re-incarnating yourself, they could give you the greased curve, while if you're brand new, you would run through the content at a normal pace.
Directed at potential complaints: If you don't like this, because you want to run 20 alts, then don't blame me, blame the game designer who set it up so that you needed to outfit 20 variants, and grind them all through the game, in order to properly enjoy yourself. Either you enjoy grinding, or the game has a design flaw.