The problem with the analogy is that while a person might see one movie last week and another movie this week and another movie a couple weeks later, MMO's tend to be exclusive of each other. If I'm just going to play a game where my character is little more than a predetermined role (tank, DPS, or buffs). I might as well just play WoW. That rigid allotment of class features by role is really a shame, as is the emphasis on combat that focuses on devising a scripted, repeatable approach to every fight.Many MMOs play it safe for the same reason Hollywood plays it safe with most movies, and why large game companies (okay WotC) also play it safe with their major properties . . . innovation is risky! Innovate well and you raise the bar and become the industry leader, innovate poorly and you destroy your once-loved property. Keep it safe and enjoy a more stable source of income and profit.
DOO needed content. It had other pros and cons, but really, without content you ain got much of an MMO>DDO (Dungeons & Dragons Online) had a lot of innovative features that were praised by critics and many players (one of which being the nonstandard D&D setting of Eberron) . . . but over time the game has morphed to be more like WoW in order to keep a survivable subscriber base. While DDOs innovations were pretty cool, the game overall was "fun" and "okay" but not "GREAT" or "OMG WOW THIS IS SO COOL!!!" and so the game never enjoyed the success it could have.