I find it funny how people defend Mojang with the strangest arguments.
Lets be serious for a Moment here, Minecraft is barely a game, it has no goal, there is ~nothing~ to do, unless you make it happen, nor does it possess a great atmosphere like Systemshock or Bioshock or any Halflife game.
Is there a sense of accomplishment as you fight trough the game, use your cunning and wits or sheer brutal power to overcome the obstacles in the game?
Has the game even an useful Tutorial or user friendly interface...not really. Are there new story arcs or new content included, well if you consider a update with an half year of development, which turned out to be bugged and just include a few minor features new content..well there you go!
Now don't get me wrong, I myself played with this toolset, even currently doing it, but do you really have "fun" like in Halflife, running alone trough an alien infested City/Lab, exploring new areas with new enemys?
Are you so into the game, having such an immersion in Games like Thief, Condemmned or Mass Effect, where you actually fear for your Character, while I myself let Steve plumming towards the ground, loosing half his livebar, because I can't be arsed to take the longer route?
I always hear people talk about the Time they are spending in Minecraft and I'm wondering, are you really having fun digging trough layers upon layers of stone, just to find a few resources here and there, that will most likely be directly fueled into your mining equipment again, just so you can mine more, because you need so much Stuff to build even the smallest things and you will never build anything small, because you want your "Imagination" to be big and presentable. Sure you spend a lot of time in Minecraft, but most of the time thats not fun.
To finish it up, I think Minecraft won't really hold his ground for that much time, in the end you will have build everything that you wanted and than that's it, there is no reasons to replay the game and nothing Notch could add would ever change that, because its a game, where you provide the fun, unlike other big games, where the Game provides fun for you, give it one or two years and Mojang is probably forgotten, maybe holding afloat with his mod community, but I just can see that the game has such a huge lifespan, if you look at the recent development speed of new content, its just ridiculous.