You're missing the point. For people who truely enjoy MMOs and are not just looking for a quick, cheap thrill, they generally ARE fun from level one. Hell, a lot of times, that's the most fun in the game.
This is what I was talking about with accomplishment-driven games. The point of the game is to get the highest level, max your skills, find the best gear, and complete all of the quests. That's what the core audience of MMORPGs is looking for. If they change that to cater to the "majority of US gamers", they'll be losing their core croud...but, more importantly, their game will no longer be an MMORPG.
Those who do not enjoy RPGs (whether online or not) for what they are, are generally the types who will never enjoy them. For instance, which of the following games did you enjoy or have fun playing: Secret of Mana? Chrono Trigger? the Ultima games? Baldur's Gate/Neverwinter Nights/Icewind Dale games? Final Fantasy 1, 2, 4, 5, 6, Mystic Quest, Adventure? Castle of the Winds? the Elder Scrolls games? Super Mario RPG? Legend of Zelda games before Majora's Mask?
These are a lot of the most well known role playing games ever. They're all accomplishment-driven, feature some aspect of grind, and have rich, entertaining stories. It's from these types of games that MMORPGs get their origins. It's from this group of players that MMORPGs find their core audience.
To make an MMORPG not accomplishment-driven is to make it not an MMORPG. To put everyone on the same plane and not give any means of character advancement, whether that be from items or character levels or skills or whatever, is to forsake the genre. What you would have is no longer an MMORPG.
Now, again, I'm not saying that one type of gaming is better than the other type. Only that they are different and cannot coexist in the same game. It's just not possible to make an MMORPG that caters to the "majority of US gamers" when those gamers prefer a game that's completely the opposite of what an MMORPG is supposed to be.
Certainly, there have been some MMORPGs that have done some things wrong (FFXI was terrible with land movement speeds, DAoC was awefully unbalanced), but even the ones that got it right still would not have been liked by the "typical US gamer". Ultima Online, for instance, before the UO:R patch was about as perfect an MMO as one could want. It was challenging, it was character-driven, it was free-form (no classes), and it combined player skill with character skill levels. It was by far the best MMORPG I ever played, yet it peaked out at about 250K subscribers. It happened early in the life of MMOs, but still. Typical US gamers simply do not look for the same elements in a game that the core audience of an MMORPG looks for, and thus the two cannot coexist.
Note: I do not currently play WoW, but I have played nearly every major market MMORPG out there starting with Ultima Online (missed Meridian 59, unfortunately) and some of the smaller ones. Also, I dislike first-person shooters so much that I cannot make it out of the first level of Half Life before I exit the game in disgust.