(Warning: plenty of irony below, as usual)
There was a time when the MMO developer community thought that the ideal was to stand up your world, and then start feeding the dragon. As quickly as possible, get new content into the players hands. The more new content, the more fascinated they would be, the stickier their subscriptions would be and the more money you would make.
So we put a lot of effort into techniques to manage continuous development of content, test it, and roll it out with the minimum possible maintenance window. Some got good enough they could release content or patches every week. Didn't we have automated client patchers? Why not use those to continuously deliver content. Not just streaming content as you move around in virtual space, but as you move forward in real time.
Then someone noticed that Walmart took their game box off the shelf because it had been there for a year, and new titles were showing up. Surely consumers want the new stuff more? Besides, you don't need the latest release, you get all the new stuff when you patch. Then new subscriptions drop because of that lack of visibility at retail. Why would Gamestop sell prepaid cards if it is so easy to pay online?
So the light goes bing, and it is suddenly obvious that sequels would be a much better approach, since you'll get shelf space if it is a new SKU. Clearly this is the best approach, since it works so well for Blizzard. (So clearly, I cannot choose the glass in front of you. Where was I?) All you have to do is patch a few bugs, and set up a parallel team to work on the sequel.
But then everyone piles onto Steam. Definitely the end of brick and mortar. Maybe we go back to the low-latency content pipeline so our game is fresher than the sequel-only guys. But wait, Steam sales and free trials increase traffic at Gamestop.
Clearly, I cannot choose the glass in front of me... Wait til I get started.
Not really. As you can see, the point is that technologists are very unlikely to see the future of sales and distribution mechanisms. And if we did, it would take a year to adapt our development practices and product design to take optimal advantage of it.
The answer? Be flexible. Don't assume you've got the one and only magic bullet. Requirements change. And for an MMO the development timespan is large enough that a lot of things will change before you are finished. Don't implement your company into a corner with a big complex optimal single point solution, and keep your mind open.